ModernDive

Chapter 4 Data Importing and “Tidy” Data

In Subsection 1.2.1, we introduced the concept of a data frame in R: a rectangular spreadsheet-like representation of data where the rows correspond to observations and the columns correspond to variables describing each observation. In Section 1.4, we started exploring our first data frame: the flights data frame included in the nycflights13 package. In Chapter 2, we created visualizations based on the data included in flights and other data frames such as weather. In Chapter 3, we learned how to take existing data frames and transform/modify them to suit our ends.

In this final chapter of the “Data Science with tidyverse” portion of the book, we extend some of these ideas by discussing a type of data formatting called “tidy” data. You will see that having data stored in “tidy” format is about more than what the everyday definition of the term “tidy” might suggest: having your data “neatly organized.” Instead, we define the term “tidy” as it’s used by data scientists who use R, outlining a set of rules by which data is saved.

Knowledge of this type of data formatting was not necessary for our treatment of data visualization in Chapter 2 and data wrangling in Chapter 3. This is because all the data used was already in “tidy” format. In this chapter, we’ll now see that this format is essential to using the tools we covered up until now. Furthermore, it will also be useful for all subsequent chapters in this book when we cover regression and statistical inference. First, however, we’ll show you how to import spreadsheet data in R.

Needed packages

Let’s load all the packages needed for this chapter (this assumes you’ve already installed them). If needed, read Section 1.3 for information on how to install and load R packages.

library(dplyr)
library(ggplot2)
library(readr)
library(tidyr)
library(nycflights13)
library(fivethirtyeight)

4.1 Importing data

Up to this point, we’ve almost entirely used data stored inside of an R package. Say instead you have your own data saved on your computer or somewhere online. How can you analyze this data in R? Spreadsheet data is often saved in one of the following three formats:

First, a Comma Separated Values .csv file. You can think of a .csv file as a bare-bones spreadsheet where:

  • Each line in the file corresponds to one row of data/one observation.
  • Values for each line are separated with commas. In other words, the values of different variables are separated by commas in each row.
  • The first line is often, but not always, a header row indicating the names of the columns/variables.

Second, an Excel .xlsx spreadsheet file. This format is based on Microsoft’s proprietary Excel software. As opposed to bare-bones .csv files, .xlsx Excel files contain a lot of meta-data (data about data). Recall we saw a previous example of meta-data in Section 3.4 when adding “group structure” meta-data to a data frame by using the group_by() verb. Some examples of Excel spreadsheet meta-data include the use of bold and italic fonts, colored cells, different column widths, and formula macros.

Third, a Google Sheets file, which is a “cloud” or online-based way to work with a spreadsheet. Google Sheets allows you to download your data in both comma separated values .csv and Excel .xlsx formats. One way to import Google Sheets data is to go to the Google Sheets menu bar -> File -> Download as -> Select “Microsoft Excel” or “Comma-separated values” and then load that data into R.

We’ll cover two methods for importing .csv and .xlsx spreadsheet data in R: one using the console and the other using RStudio’s graphical user interface, abbreviated as “GUI.”

4.1.1 Using the console

First, let’s import a Comma Separated Values .csv file that exists on the internet. The .csv file dem_score.csv contains ratings of the level of democracy in different countries spanning 1952 to 1992 and is accessible at https://moderndive.com/data/dem_score.csv. Let’s use the read_csv() function from the readr (Wickham, Hester, and Francois 2018) package to read it off the web, import it into R, and save it in a data frame called dem_score.

library(readr)
dem_score <- read_csv("https://moderndive.com/data/dem_score.csv")
dem_score
# A tibble: 96 x 10
   country    `1952` `1957` `1962` `1967` `1972` `1977` `1982` `1987` `1992`
   <chr>       <dbl>  <dbl>  <dbl>  <dbl>  <dbl>  <dbl>  <dbl>  <dbl>  <dbl>
 1 Albania        -9     -9     -9     -9     -9     -9     -9     -9      5
 2 Argentina      -9     -1     -1     -9     -9     -9     -8      8      7
 3 Armenia        -9     -7     -7     -7     -7     -7     -7     -7      7
 4 Australia      10     10     10     10     10     10     10     10     10
 5 Austria        10     10     10     10     10     10     10     10     10
 6 Azerbaijan     -9     -7     -7     -7     -7     -7     -7     -7      1
 7 Belarus        -9     -7     -7     -7     -7     -7     -7     -7      7
 8 Belgium        10     10     10     10     10     10     10     10     10
 9 Bhutan        -10    -10    -10    -10    -10    -10    -10    -10    -10
10 Bolivia        -4     -3     -3     -4     -7     -7      8      9      9
# … with 86 more rows

In this dem_score data frame, the minimum value of -10 corresponds to a highly autocratic nation, whereas a value of 10 corresponds to a highly democratic nation. Note also that backticks surround the different variable names. Variable names in R by default are not allowed to start with a number nor include spaces, but we can get around this fact by surrounding the column name with backticks. We’ll revisit the dem_score data frame in a case study in the upcoming Section 4.3.

Note that the read_csv() function included in the readr package is different than the read.csv() function that comes installed with R. While the difference in the names might seem trivial (an _ instead of a .), the read_csv() function is, in our opinion, easier to use since it can more easily read data off the web and generally imports data at a much faster speed. Furthermore, the read_csv() function included in the readr saves data frames as tibbles by default. tibble is short for “tidy table”; we’ll discuss what it takes for data to be “tidy” shortly in the upcoming Section 4.2.

4.1.2 Using RStudio’s interface

Let’s read in the exact same data, but this time from an Excel file saved on your computer. Furthermore, we’ll do this using RStudio’s graphical interface instead of running read_csv() in the console. First, download the Excel file dem_score.xlsx by going to https://moderndive.com/data/dem_score.xlsx, then

  1. Go to the Files pane of RStudio.
  2. Navigate to the directory (i.e., folder on your computer) where the downloaded dem_score.xlsx Excel file is saved. For example, this might be in your Downloads folder.
  3. Click on dem_score.xlsx.
  4. Click “Import Dataset…”

At this point, you should see a screen pop-up like in Figure 4.1. After clicking on the “Import” button on the bottom right of Figure 4.1, RStudio will save this spreadsheet’s data in a data frame called dem_score and display its contents in the spreadsheet viewer.

Importing an Excel file to R.

FIGURE 4.1: Importing an Excel file to R.

Furthermore, note the “Code Preview” block in the bottom right of Figure 4.1. You can copy and paste this code to reload your data again later programmatically, instead of repeating this manual point-and-click process.

4.2 Tidy data

Let’s now switch gears and learn about the concept of “tidy” data format with a motivating example from the fivethirtyeight package. The fivethirtyeight package (Kim, Ismay, and Chunn 2019) provides access to the datasets used in many articles published by the data journalism website, FiveThirtyEight.com. For a complete list of all 127 datasets included in the fivethirtyeight package, check out the package webpage by going to: https://fivethirtyeight-r.netlify.com/articles/fivethirtyeight.html.

Let’s focus our attention on the drinks data frame and look at its first 5 rows:

# A tibble: 5 x 5
  country    beer_servings spirit_servings wine_servings total_litres_of_pure_a…
  <chr>              <int>           <int>         <int>                   <dbl>
1 Afghanist…             0               0             0                     0  
2 Albania               89             132            54                     4.9
3 Algeria               25               0            14                     0.7
4 Andorra              245             138           312                    12.4
5 Angola               217              57            45                     5.9

After reading the help file by running ?drinks, you’ll see that drinks is a data frame containing results from a survey of the average number of servings of beer, spirits, and wine consumed in 193 countries. This data was originally reported on FiveThirtyEight.com in Mona Chalabi’s article: “Dear Mona Followup: Where Do People Drink The Most Beer, Wine And Spirits?”.

Let’s apply some of the data wrangling verbs we learned in Chapter 3 on the drinks data frame:

  1. filter() the drinks data frame to only consider 4 countries: the United States, China, Italy, and Saudi Arabia, then
  2. select() all columns except total_litres_of_pure_alcohol by using the - sign, then
  3. rename() the variables beer_servings, spirit_servings, and wine_servings to beer, spirit, and wine, respectively.

and save the resulting data frame in drinks_smaller:

drinks_smaller <- drinks %>% 
  filter(country %in% c("USA", "China", "Italy", "Saudi Arabia")) %>% 
  select(-total_litres_of_pure_alcohol) %>% 
  rename(beer = beer_servings, spirit = spirit_servings, wine = wine_servings)
drinks_smaller
# A tibble: 4 x 4
  country       beer spirit  wine
  <chr>        <int>  <int> <int>
1 China           79    192     8
2 Italy           85     42   237
3 Saudi Arabia     0      5     0
4 USA            249    158    84

Let’s now ask ourselves a question: “Using the drinks_smaller data frame, how would we create the side-by-side barplot in Figure 4.2?”. Recall we saw barplots displaying two categorical variables in Subsection 2.8.3.

Comparing alcohol consumption in 4 countries.

FIGURE 4.2: Comparing alcohol consumption in 4 countries.

Let’s break down the grammar of graphics we introduced in Section 2.1:

  1. The categorical variable country with four levels (China, Italy, Saudi Arabia, USA) would have to be mapped to the x-position of the bars.
  2. The numerical variable servings would have to be mapped to the y-position of the bars (the height of the bars).
  3. The categorical variable type with three levels (beer, spirit, wine) would have to be mapped to the fill color of the bars.

Observe, however, that drinks_smaller has three separate variables beer, spirit, and wine. In order to use the ggplot() function to recreate the barplot in Figure 4.2; however, we need a single variable type with three possible values: beer, spirit, and wine. We could then map this type variable to the fill aesthetic of our plot. In other words, to recreate the barplot in Figure 4.2, our data frame would have to look like this:

drinks_smaller_tidy
# A tibble: 12 x 3
   country      type   servings
   <chr>        <chr>     <int>
 1 China        beer         79
 2 Italy        beer         85
 3 Saudi Arabia beer          0
 4 USA          beer        249
 5 China        spirit      192
 6 Italy        spirit       42
 7 Saudi Arabia spirit        5
 8 USA          spirit      158
 9 China        wine          8
10 Italy        wine        237
11 Saudi Arabia wine          0
12 USA          wine         84

Let’s compare drinks_smaller_tidy to the drinks_smaller data frame from earlier:

drinks_smaller
# A tibble: 4 x 4
  country       beer spirit  wine
  <chr>        <int>  <int> <int>
1 China           79    192     8
2 Italy           85     42   237
3 Saudi Arabia     0      5     0
4 USA            249    158    84

Observe that while drinks_smaller and drinks_smaller_tidy are both rectangular in shape and contain the same 12 numerical values (3 alcohol types by 4 countries), they are formatted differently. drinks_smaller is formatted in what’s known as “wide” format, whereas drinks_smaller_tidy is formatted in what’s known as “long/narrow” format.

In the context of doing data science in R, long/narrow format is also known as “tidy” format. In order to use the ggplot2 and dplyr packages for data visualization and data wrangling, your input data frames must be in “tidy” format. Thus, all non-“tidy” data must be converted to “tidy” format first.

Before we show you how to convert non-“tidy” data frames like drinks_smaller to “tidy” data frames like drinks_smaller_tidy, let’s go over the explicit definition of “tidy” data.

4.2.1 Definition of “tidy” data

You have surely heard the word “tidy” in your life:

What does it mean for your data to be “tidy”? While “tidy” has a clear English meaning of “organized,” the word “tidy” in the context of data science using R means that your data follows a standardized format. We will follow Hadley Wickham’s definition of tidy data (Wickham 2014) and the subsequent diagram in Figure 4.3:

A dataset is a collection of values, usually either numbers (if quantitative) or strings AKA text data (if qualitative/categorical). Values are organised in two ways. Every value belongs to a variable and an observation. A variable contains all values that measure the same underlying attribute (like height, temperature, duration) across units. An observation contains all values measured on the same unit (like a person, or a day, or a city) across attributes.

“Tidy” data is a standard way of mapping the meaning of a dataset to its structure. A dataset is messy or tidy depending on how rows, columns and tables are matched up with observations, variables and types. In tidy data:

  1. Each variable forms a column.
  2. Each observation forms a row.
  3. Each type of observational unit forms a table.
Tidy data graphic from R for Data Science.

FIGURE 4.3: Tidy data graphic from R for Data Science.

For example, say you have the following table of stock prices in Table 4.1:

TABLE 4.1: Stock prices (non-tidy format)
Date Boeing stock price Amazon stock price Google stock price
2009-01-01 $173.55 $174.90 $174.34
2009-01-02 $172.61 $171.42 $170.04

Although the data are neatly organized in a rectangular spreadsheet-type format, they do not follow the definition of data in “tidy” format. While there are three variables corresponding to three unique pieces of information (date, stock name, and stock price), there are not three columns. In “tidy” data format, each variable should be its own column, as shown in Table 4.2. Notice that both tables present the same information, but in different formats.

TABLE 4.2: Stock prices (tidy format)
Date Stock Name Stock Price
2009-01-01 Boeing $173.55
2009-01-01 Amazon $174.90
2009-01-01 Google $174.34
2009-01-02 Boeing $172.61
2009-01-02 Amazon $171.42
2009-01-02 Google $170.04

Now we have the requisite three columns Date, Stock Name, and Stock Price. On the other hand, consider the data in Table 4.3.

TABLE 4.3: Example of tidy data
Date Boeing Price Weather
2009-01-01 $173.55 Sunny
2009-01-02 $172.61 Overcast

In this case, even though the variable “Boeing Price” occurs just like in our non-“tidy” data in Table 4.1, the data is “tidy” since there are three variables corresponding to three unique pieces of information: Date, Boeing price, and the Weather that particular day.

Learning check

(LC4.1) What are common characteristics of “tidy” data frames?

(LC4.2) What makes “tidy” data frames useful for organizing data?

4.2.2 Converting to “tidy” data

In this book so far, you’ve only seen data frames that were already in “tidy” format. Furthermore, for the rest of this book, you’ll mostly only see data frames that are already in “tidy” format as well. This is not always the case however with all datasets in the world. If your original data frame is in wide (non-“tidy”) format and you would like to use the ggplot2 or dplyr packages, you will first have to convert it to “tidy” format. To do so, we recommend using the pivot_longer() function in the tidyr package (Wickham and Henry 2019).

Going back to our drinks_smaller data frame from earlier:

drinks_smaller
# A tibble: 4 x 4
  country       beer spirit  wine
  <chr>        <int>  <int> <int>
1 China           79    192     8
2 Italy           85     42   237
3 Saudi Arabia     0      5     0
4 USA            249    158    84

We convert it to “tidy” format by using the pivot_longer() function from the tidyr package as follows:

drinks_smaller_tidy <- drinks_smaller %>% 
  pivot_longer(names_to = "type", 
               values_to = "servings", 
               cols = -country)
drinks_smaller_tidy
# A tibble: 12 x 3
   country      type   servings
   <chr>        <chr>     <int>
 1 China        beer         79
 2 China        spirit      192
 3 China        wine          8
 4 Italy        beer         85
 5 Italy        spirit       42
 6 Italy        wine        237
 7 Saudi Arabia beer          0
 8 Saudi Arabia spirit        5
 9 Saudi Arabia wine          0
10 USA          beer        249
11 USA          spirit      158
12 USA          wine         84

We set the arguments to pivot_longer() as follows:

  1. names_to here corresponds to the name of the variable in the new tidy/long data frame that will contain the column names of the original data. Observe how we set names_to = "type". In the resulting drinks_smaller_tidy, the column type contains the three types of alcohol beer, spirit, and wine. Since type is a variable name that doesn’t appear in drinks_smaller, we use quotation marks around it. You’ll receive an error if you just use names_to = type here.
  2. values_to here is the name of the variable in the new tidy data frame that will contain the values of the original data. Observe how we set values_to = "servings" since each of the numeric values in each of the beer, wine, and spirit columns of the drinks_smaller data corresponds to a value of servings. In the resulting drinks_smaller_tidy, the column servings contains the 4 \(\times\) 3 = 12 numerical values. Note again that servings doesn’t appear as a variable in drinks_smaller so it again needs quotation marks around it for the values_to argument.
  3. The third argument cols is the columns in the drinks_smaller data frame you either want to or don’t want to tidy. Observe how we set this to -country indicating that we don’t want to tidy the country variable in drinks_smaller and rather only beer, spirit, and wine. Since country is a column that appears in drinks_smaller we don’t put quotation marks around it.

The third argument here of cols is a little nuanced, so let’s consider code that’s written slightly differently but that produces the same output:

drinks_smaller %>% 
  pivot_longer(names_to = "type", 
               values_to = "servings", 
               cols = c(beer, spirit, wine))

Note that the third argument now specifies which columns we want to tidy with c(beer, spirit, wine), instead of the columns we don’t want to tidy using -country. We use the c() function to create a vector of the columns in drinks_smaller that we’d like to tidy. Note that since these three columns appear one after another in the drinks_smaller data frame, we could also do the following for the cols argument:

drinks_smaller %>% 
  pivot_longer(names_to = "type", 
               values_to = "servings", 
               cols = beer:wine)

With our drinks_smaller_tidy “tidy” formatted data frame, we can now produce the barplot you saw in Figure 4.2 using geom_col(). This is done in Figure 4.4. Recall from Section 2.8 on barplots that we use geom_col() and not geom_bar(), since we would like to map the “pre-counted” servings variable to the y-aesthetic of the bars.

ggplot(drinks_smaller_tidy, 
       aes(x = country, y = servings, fill = type)) +
  geom_col(position = "dodge")
Comparing alcohol consumption in 4 countries using geom_col().

FIGURE 4.4: Comparing alcohol consumption in 4 countries using geom_col().

Converting “wide” format data to “tidy” format often confuses new R users. The only way to learn to get comfortable with the pivot_longer() function is with practice, practice, and more practice using different datasets. For example, run ?pivot_longer and look at the examples in the bottom of the help file. We’ll show another example of using pivot_longer() to convert a “wide” formatted data frame to “tidy” format in Section 4.3.

If however you want to convert a “tidy” data frame to “wide” format, you will need to use the pivot_wider() function instead. Run ?pivot_wider and look at the examples in the bottom of the help file for examples.

You can also view examples of both pivot_longer() and pivot_wider() on the tidyverse.org webpage. There’s a nice example to check out the different functions available for data tidying and a case study using data from the World Health Organization on that webpage. Each week the R4DS Online Learning Community posts a data set in the weekly #TidyTuesday event that might serve as a nice place for you to find other data to explore and transform.

Learning check

(LC4.3) Take a look at the airline_safety data frame included in the fivethirtyeight data package. Run the following:

airline_safety

After reading the help file by running ?airline_safety, we see that airline_safety is a data frame containing information on different airline companies’ safety records. This data was originally reported on the data journalism website, FiveThirtyEight.com, in Nate Silver’s article, “Should Travelers Avoid Flying Airlines That Have Had Crashes in the Past?”. Let’s ignore the incl_reg_subsidiaries and avail_seat_km_per_week variables for simplicity:

airline_safety_smaller <- airline_safety %>% 
  select(-c(incl_reg_subsidiaries, avail_seat_km_per_week))
airline_safety_smaller
# A tibble: 56 x 7
   airline incidents_85_99 fatal_accidents… fatalities_85_99 incidents_00_14
   <chr>             <int>            <int>            <int>           <int>
 1 Aer Li…               2                0                0               0
 2 Aerofl…              76               14              128               6
 3 Aeroli…               6                0                0               1
 4 Aerome…               3                1               64               5
 5 Air Ca…               2                0                0               2
 6 Air Fr…              14                4               79               6
 7 Air In…               2                1              329               4
 8 Air Ne…               3                0                0               5
 9 Alaska…               5                0                0               5
10 Alital…               7                2               50               4
# … with 46 more rows, and 2 more variables: fatal_accidents_00_14 <int>,
#   fatalities_00_14 <int>

This data frame is not in “tidy” format. How would you convert this data frame to be in “tidy” format, in particular so that it has a variable incident_type_years indicating the incident type/year and a variable count of the counts?

4.2.3 nycflights13 package

Recall the nycflights13 package we introduced in Section 1.4 with data about all domestic flights departing from New York City in 2013. Let’s revisit the flights data frame by running View(flights). We saw that flights has a rectangular shape, with each of its 336,776 rows corresponding to a flight and each of its 22 columns corresponding to different characteristics/measurements of each flight. This satisfied the first two criteria of the definition of “tidy” data from Subsection 4.2.1: that “Each variable forms a column” and “Each observation forms a row.” But what about the third property of “tidy” data that “Each type of observational unit forms a table”?

Recall that we also saw in Subsection 1.4.3 that the observational unit for the flights data frame is an individual flight. In other words, the rows of the flights data frame refer to characteristics/measurements of individual flights. Also included in the nycflights13 package are other data frames with their rows representing different observational units (Wickham 2019):

  • airlines: translation between two letter IATA carrier codes and airline company names (16 in total). The observational unit is an airline company.
  • planes: aircraft information about each of 3,322 planes used, i.e., the observational unit is an aircraft.
  • weather: hourly meteorological data (about 8705 observations) for each of the three NYC airports, i.e., the observational unit is an hourly measurement of weather at one of the three airports.
  • airports: airport names and locations. The observational unit is an airport.

The organization of the information into these five data frames follows the third “tidy” data property: observations corresponding to the same observational unit should be saved in the same table, i.e., data frame. You could think of this property as the old English expression: “birds of a feather flock together.”

4.3 Case study: Democracy in Guatemala

In this section, we’ll show you another example of how to convert a data frame that isn’t in “tidy” format (“wide” format) to a data frame that is in “tidy” format (“long/narrow” format). We’ll do this using the pivot_longer() function from the tidyr package again.

Furthermore, we’ll make use of functions from the ggplot2 and dplyr packages to produce a time-series plot showing how the democracy scores have changed over the 40 years from 1952 to 1992 for Guatemala. Recall that we saw time-series plots in Section 2.4 on creating linegraphs using geom_line().

Let’s use the dem_score data frame we imported in Section 4.1, but focus on only data corresponding to Guatemala.

guat_dem <- dem_score %>% 
  filter(country == "Guatemala")
guat_dem
# A tibble: 1 x 10
  country   `1952` `1957` `1962` `1967` `1972` `1977` `1982` `1987` `1992`
  <chr>      <dbl>  <dbl>  <dbl>  <dbl>  <dbl>  <dbl>  <dbl>  <dbl>  <dbl>
1 Guatemala      2     -6     -5      3      1     -3     -7      3      3

Let’s lay out the grammar of graphics we saw in Section 2.1.

First we know we need to set data = guat_dem and use a geom_line() layer, but what is the aesthetic mapping of variables? We’d like to see how the democracy score has changed over the years, so we need to map:

  • year to the x-position aesthetic and
  • democracy_score to the y-position aesthetic

Now we are stuck in a predicament, much like with our drinks_smaller example in Section 4.2. We see that we have a variable named country, but its only value is "Guatemala". We have other variables denoted by different year values. Unfortunately, the guat_dem data frame is not “tidy” and hence is not in the appropriate format to apply the grammar of graphics, and thus we cannot use the ggplot2 package just yet.

We need to take the values of the columns corresponding to years in guat_dem and convert them into a new “key” variable called year. Furthermore, we need to take the democracy score values in the inside of the data frame and turn them into a new “value” variable called democracy_score. Our resulting data frame will thus have three columns: country, year, and democracy_score. Recall that the pivot_longer() function in the tidyr package can complete this task for us:

guat_dem_tidy <- guat_dem %>% 
  pivot_longer(names_to = "year", 
               values_to = "democracy_score", 
               cols = -country,
               names_ptypes = list(year = integer())) 
guat_dem_tidy
# A tibble: 9 x 3
  country    year democracy_score
  <chr>     <int>           <dbl>
1 Guatemala  1952               2
2 Guatemala  1957              -6
3 Guatemala  1962              -5
4 Guatemala  1967               3
5 Guatemala  1972               1
6 Guatemala  1977              -3
7 Guatemala  1982              -7
8 Guatemala  1987               3
9 Guatemala  1992               3

We set the arguments to pivot_longer() as follows:

  1. names_to is the name of the variable in the new “tidy” data frame that will contain the column names of the original data. Observe how we set names_to = "year". In the resulting guat_dem_tidy, the column year contains the years where Guatemala’s democracy scores were measured.
  2. values_to is the name of the variable in the new “tidy” data frame that will contain the values of the original data. Observe how we set values_to = "democracy_score". In the resulting guat_dem_tidy the column democracy_score contains the 1 \(\times\) 9 = 9 democracy scores as numeric values.
  3. The third argument is the columns you either want to or don’t want to tidy. Observe how we set this to cols = -country indicating that we don’t want to tidy the country variable in guat_dem and rather only variables 1952 through 1992.
  4. The last argument of names_ptypes tells R what type of variable year should be set to. Without specifying that it is an integer as we’ve done here, pivot_longer() will set it to be a character value by default.

We can now create the time-series plot in Figure 4.5 to visualize how democracy scores in Guatemala have changed from 1952 to 1992 using a geom_line().

ggplot(guat_dem_tidy, aes(x = year, y = democracy_score)) +
  geom_line() +
  labs(x = "Year", y = "Democracy Score")
Democracy scores in Guatemala 1952-1992.

FIGURE 4.5: Democracy scores in Guatemala 1952-1992.

Note that if we forgot to include the names_ptypes argument specifying that year was not of character format, we would have gotten an error here since geom_line() wouldn’t have known how to sort the characters in the right order.

Learning check

(LC4.4) Convert the dem_score data frame into a tidy data frame and assign the name of dem_score_tidy to the resulting long-formatted data frame.

(LC4.5) Read in the life expectancy data stored at https://moderndive.com/data/le_mess.csv and convert it to a tidy data frame.

4.4 tidyverse package

Notice at the beginning of the chapter we loaded the following four packages, which are among four of the most frequently used R packages for data science:

library(dplyr)
library(ggplot2)
library(readr)
library(tidyr)

There is a much quicker way to load these packages than by individually loading them: by installing and loading the tidyverse package. The tidyverse package acts as an “umbrella” package whereby installing/loading it will install/load multiple packages at once for you.

After installing the tidyverse package as you would a normal package via install.packages("tidyverse"), running:

library(tidyverse)

would be the same as running:

library(ggplot2)
library(dplyr)
library(tidyr)
library(readr)
library(purrr)
library(tibble)
library(stringr)
library(forcats)

You’ve seen the first four of these packages: ggplot2 for data visualization, dplyr for data wrangling, tidyr for converting data to “tidy” format, and readr for importing spreadsheet data into R. The remaining packages (purrr, tibble, stringr, and forcats) are left for a more advanced book; check out R for Data Science to learn about these packages.

For the remainder of this book, we’ll start every chapter by running library(tidyverse), instead of loading the various component packages individually. The tidyverse “umbrella” package gets its name from the fact that all the functions in all its packages are designed to have common inputs and outputs: data frames are in “tidy” format. This standardization of input and output data frames makes transitions between different functions in the different packages as seamless as possible. For more information, check out the tidyverse.org webpage for the package.

4.5 Conclusion

4.5.1 Additional resources

An R script file of all R code used in this chapter is available here.

If you want to learn more about using the readr and tidyr package, we suggest that you check out RStudio’s “Data Import Cheat Sheet.” In the current version of RStudio in late 2019, you can access this cheatsheet by going to the RStudio Menu Bar -> Help -> Cheatsheets -> “Browse Cheatsheets” -> Scroll down the page to the “Data Import Cheat Sheet.” The first page of this cheatsheet has information on using the readr package to import data, while the second page has information on using the tidyr package to “tidy” data. You can see a preview of both cheatsheets in the figures below.

Data Import cheatsheet (first page): readr package.

FIGURE 4.6: Data Import cheatsheet (first page): readr package.

Data Import cheatsheet (second page): tidyr package.

FIGURE 4.7: Data Import cheatsheet (second page): tidyr package.

4.5.2 What’s to come?

Congratulations! You’ve completed the “Data Science with tidyverse” portion of this book. We’ll now move to the “Data modeling with moderndive” portion of this book in Chapters 5 and 6, where you’ll leverage your data visualization and wrangling skills to model relationships between different variables in data frames.

However, we’re going to leave Chapter 10 on “Inference for Regression” until after we’ve covered statistical inference in Chapters 7, 8, and 9. Onwards and upwards into Data Modeling as shown in Figure 4.8!

ModernDive flowchart - on to Part II!

FIGURE 4.8: ModernDive flowchart - on to Part II!

References

Kim, Albert Y., Chester Ismay, and Jennifer Chunn. 2019. Fivethirtyeight: Data and Code Behind the Stories and Interactives at ’Fivethirtyeight’. https://CRAN.R-project.org/package=fivethirtyeight.

Wickham, Hadley. 2014. “Tidy Data.” Journal of Statistical Software Volume 59 (Issue 10). https://www.jstatsoft.org/index.php/jss/article/view/v059i10/v59i10.pdf.

Wickham, Hadley. 2019. Nycflights13: Flights That Departed Nyc in 2013. https://CRAN.R-project.org/package=nycflights13.

Wickham, Hadley, and Lionel Henry. 2019. Tidyr: Tidy Messy Data. https://CRAN.R-project.org/package=tidyr.

Wickham, Hadley, Jim Hester, and Romain Francois. 2018. Readr: Read Rectangular Text Data. https://CRAN.R-project.org/package=readr.