Data Wrangling with dplyr and tidyr
Last updated on 2024-04-30 | Edit this page
Overview
Questions
- How can I select specific rows and/or columns from a dataframe?
- How can I combine multiple commands into a single command?
- How can I create new columns or remove existing columns from a dataframe?
- How can I reformat a dataframe to meet my needs?
Objectives
- Describe the purpose of an R package and the
dplyrandtidyrpackages. - Select certain columns in a dataframe with the
dplyrfunctionselect. - Select certain rows in a dataframe according to filtering conditions
with the
dplyrfunctionfilter. - Link the output of one
dplyrfunction to the input of another function with the ‘pipe’ operator%>%. - Add new columns to a dataframe that are functions of existing
columns with
mutate. - Use the split-apply-combine concept for data analysis.
- Use
summarize,group_by, andcountto split a dataframe into groups of observations, apply a summary statistics for each group, and then combine the results. - Describe the concept of a wide and a long table format and for which purpose those formats are useful.
- Describe the roles of variable names and their associated values when a table is reshaped.
- Reshape a dataframe from long to wide format and back with the
pivot_widerandpivot_longercommands from thetidyrpackage. - Export a dataframe to a csv file.
dplyr is a package for making tabular
data wrangling easier by using a limited set of functions that can be
combined to extract and summarize insights from your data. It pairs
nicely with tidyr which enables you to
swiftly convert between different data formats (long vs. wide) for
plotting and analysis.
Similarly to readr,
dplyr and
tidyr are also part of the tidyverse.
These packages were loaded in R’s memory when we called
library(tidyverse) earlier.
Note
The packages in the tidyverse, namely
dplyr, tidyr
and ggplot2 accept both the British
(e.g. summarise) and American (e.g. summarize)
spelling variants of different function and option names. For this
lesson, we utilize the American spellings of different functions;
however, feel free to use the regional variant for where you are
teaching.
What is an R package?
The package dplyr provides easy tools
for the most common data wrangling tasks. It is built to work directly
with dataframes, with many common tasks optimized by being written in a
compiled language (C++) (not all R packages are written in R!).
The package tidyr addresses the common
problem of wanting to reshape your data for plotting and use by
different R functions. Sometimes we want data sets where we have one row
per measurement. Sometimes we want a dataframe where each measurement
type has its own column, and rows are instead more aggregated groups.
Moving back and forth between these formats is nontrivial, and
tidyr gives you tools for this and more
sophisticated data wrangling.
But there are also packages available for a wide range of tasks
including building plots (ggplot2, which
we’ll see later), downloading data from the NCBI database, or performing
statistical analysis on your data set. Many packages such as these are
housed on, and downloadable from, the Comprehensive
R Archive Network
(CRAN) using install.packages. This function makes the
package accessible by your R installation with the command
library(), as you did with tidyverse
earlier.
To easily access the documentation for a package within R or RStudio,
use help(package = "package_name").
To learn more about dplyr and
tidyr after the workshop, you may want to
check out this handy
data transformation with dplyr
cheatsheet and this one
about tidyr.
Learning dplyr and
tidyr
We are working with the same dataset as earlier. Refer to the previous lesson to download the data, if you do not have it loaded.
We’re going to learn some of the most common
dplyr functions:
-
select(): subset columns -
filter(): subset rows on conditions -
mutate(): create new columns by using information from other columns -
group_by()andsummarize(): create summary statistics on grouped data -
arrange(): sort results -
count(): count discrete values
Selecting columns and filtering rows
To select columns of a dataframe, use select(). The
first argument to this function is the dataframe
(movieSerie), and the subsequent arguments are the columns
to keep, separated by commas. Alternatively, if you are selecting
columns adjacent to each other, you can use a : to select a
range of columns, read as “select columns from ___ to ___.”
R
# to select columns throughout the dataframe
select(movieSerie, title, description)
OUTPUT
# A tibble: 5,850 × 2
title description
<chr> <chr>
1 Five Came Back: The Reference Films "This collection includes 12 World War I…
2 Taxi Driver "A mentally unstable Vietnam War veteran…
3 Deliverance "Intent on seeing the Cahulawassee River…
4 Monty Python and the Holy Grail "King Arthur, accompanied by his squire,…
5 The Dirty Dozen "12 American military prisoners in World…
6 Monty Python's Flying Circus "A British sketch comedy series with the…
7 Life of Brian "Brian Cohen is an average young Jewish …
8 Dirty Harry "When a madman dubbed 'Scorpio' terroriz…
9 Bonnie and Clyde "In the 1930s, bored waitress Bonnie Par…
10 The Blue Lagoon "Two small children and a ship's cook su…
# ℹ 5,840 more rowsR
# to select a series of connected columns
select(movieSerie, title:description)
OUTPUT
# A tibble: 5,850 × 4
title type genre description
<chr> <chr> <chr> <chr>
1 Five Came Back: The Reference Films SHOW documentation "This collection inc…
2 Taxi Driver MOVIE drama "A mentally unstable…
3 Deliverance MOVIE drama "Intent on seeing th…
4 Monty Python and the Holy Grail MOVIE fantasy "King Arthur, accomp…
5 The Dirty Dozen MOVIE war "12 American militar…
6 Monty Python's Flying Circus SHOW comedy "A British sketch co…
7 Life of Brian MOVIE comedy "Brian Cohen is an a…
8 Dirty Harry MOVIE thriller "When a madman dubbe…
9 Bonnie and Clyde MOVIE crime "In the 1930s, bored…
10 The Blue Lagoon MOVIE romance "Two small children …
# ℹ 5,840 more rowsTo choose rows based on specific criteria, we can use the
filter() function. The argument after the dataframe is the
condition we want our final dataframe to adhere to
(e.g. age_certification is PG-13):
R
# filters observations where age_certification name is "PG-13"
filter(movieSerie, age_certification == "PG-13")
OUTPUT
# A tibble: 451 × 14
id title type genre description release_year age_certification runtime
<chr> <chr> <chr> <chr> <chr> <dbl> <chr> <dbl>
1 tm67378 The … MOVIE west… "An arroga… 1966 PG-13 117
2 tm145608 Awak… MOVIE drama "Dr. Malco… 1990 PG-13 120
3 tm147710 Nati… MOVIE come… "It's Chri… 1989 PG-13 97
4 tm142895 Lean… MOVIE drama "When prin… 1989 PG-13 105
5 tm107744 Miss… MOVIE thri… "When Etha… 1996 PG-13 110
6 tm122434 Forr… MOVIE drama "A man wit… 1994 PG-13 142
7 tm191110 Tita… MOVIE drama "101-year-… 1997 PG-13 194
8 tm27395 Miss… MOVIE thri… "With comp… 2000 PG-13 123
9 tm113513 Dumb… MOVIE come… "Lloyd and… 1994 PG-13 107
10 tm192405 Gatt… MOVIE scifi "In a futu… 1997 PG-13 106
# ℹ 441 more rows
# ℹ 6 more variables: seasons <dbl>, imdb_id <chr>, imdb_score <dbl>,
# imdb_votes <dbl>, tmdb_popularity <dbl>, tmdb_score <dbl>We can also specify multiple conditions within the
filter() function. We can combine conditions using either
“and” or “or” statements. In an “and” statement, an observation (row)
must meet every criteria to be included in the
resulting dataframe. To form “and” statements within dplyr, we can pass
our desired conditions as arguments in the filter()
function, separated by commas:
R
# filters observations with "and" operator (comma)
# output dataframe satisfies ALL specified conditions
filter(movieSerie, age_certification == "PG-13",
runtime > 100,
imdb_score < 6.0)
OUTPUT
# A tibble: 60 × 14
id title type genre description release_year age_certification runtime
<chr> <chr> <chr> <chr> <chr> <dbl> <chr> <dbl>
1 tm12499 The … MOVIE thri… "Angela Be… 1995 PG-13 114
2 tm93055 Grow… MOVIE come… "After the… 2010 PG-13 102
3 tm159901 Miss… MOVIE acti… "After her… 2005 PG-13 115
4 tm88045 How … MOVIE come… "After bei… 2010 PG-13 121
5 tm700 10,0… MOVIE acti… "A prehist… 2008 PG-13 109
6 tm39487 Catc… MOVIE drama "Gray Whee… 2006 PG-13 111
7 tm130574 Did … MOVIE come… "In New Yo… 2009 PG-13 103
8 tm148041 What… MOVIE come… "What's Yo… 2009 PG-13 192
9 tm237621 The … MOVIE horr… "Two buddi… 2009 PG-13 122
10 tm59289 Rowd… MOVIE acti… "A small-t… 2012 PG-13 143
# ℹ 50 more rows
# ℹ 6 more variables: seasons <dbl>, imdb_id <chr>, imdb_score <dbl>,
# imdb_votes <dbl>, tmdb_popularity <dbl>, tmdb_score <dbl>We can also form “and” statements with the &
operator instead of commas:
R
# filters observations with "&" logical operator
# output dataframe satisfies ALL specified conditions
filter(movieSerie, age_certification == "PG-13" &
runtime > 100 &
imdb_score < 6.0)
OUTPUT
# A tibble: 60 × 14
id title type genre description release_year age_certification runtime
<chr> <chr> <chr> <chr> <chr> <dbl> <chr> <dbl>
1 tm12499 The … MOVIE thri… "Angela Be… 1995 PG-13 114
2 tm93055 Grow… MOVIE come… "After the… 2010 PG-13 102
3 tm159901 Miss… MOVIE acti… "After her… 2005 PG-13 115
4 tm88045 How … MOVIE come… "After bei… 2010 PG-13 121
5 tm700 10,0… MOVIE acti… "A prehist… 2008 PG-13 109
6 tm39487 Catc… MOVIE drama "Gray Whee… 2006 PG-13 111
7 tm130574 Did … MOVIE come… "In New Yo… 2009 PG-13 103
8 tm148041 What… MOVIE come… "What's Yo… 2009 PG-13 192
9 tm237621 The … MOVIE horr… "Two buddi… 2009 PG-13 122
10 tm59289 Rowd… MOVIE acti… "A small-t… 2012 PG-13 143
# ℹ 50 more rows
# ℹ 6 more variables: seasons <dbl>, imdb_id <chr>, imdb_score <dbl>,
# imdb_votes <dbl>, tmdb_popularity <dbl>, tmdb_score <dbl>In an “or” statement, observations must meet at least one of the specified conditions. To form “or” statements we use the logical operator for “or,” which is the vertical bar (|):
R
# filters observations with "|" logical operator
# output dataframe satisfies AT LEAST ONE of the specified conditions
filter(movieSerie, age_certification == "PG-13" |
runtime > 100 |
imdb_score < 6.0)
OUTPUT
# A tibble: 2,852 × 14
id title type genre description release_year age_certification runtime
<chr> <chr> <chr> <chr> <chr> <dbl> <chr> <dbl>
1 tm84618 Taxi… MOVIE drama A mentally… 1976 "R" 114
2 tm154986 Deli… MOVIE drama Intent on … 1972 "R" 109
3 tm120801 The … MOVIE war 12 America… 1967 "" 150
4 tm14873 Dirt… MOVIE thri… When a mad… 1971 "R" 102
5 tm119281 Bonn… MOVIE crime In the 193… 1967 "R" 110
6 tm98978 The … MOVIE roma… Two small … 1980 "R" 104
7 tm44204 The … MOVIE acti… A team of … 1961 "" 158
8 tm67378 The … MOVIE west… An arrogan… 1966 "PG-13" 117
9 tm16479 Whit… MOVIE roma… Two talent… 1954 "" 115
10 tm89386 Hitl… MOVIE hist… A keen chr… 1977 "PG" 150
# ℹ 2,842 more rows
# ℹ 6 more variables: seasons <dbl>, imdb_id <chr>, imdb_score <dbl>,
# imdb_votes <dbl>, tmdb_popularity <dbl>, tmdb_score <dbl>Pipes
What if you want to select and filter at the same time? There are three ways to do this: use intermediate steps, nested functions, or pipes.
With intermediate steps, you create a temporary dataframe and use that as input to the next function, like this:
R
movieSerie2 <- filter(movieSerie, age_certification == "PG-13")
movieSerie_ch <- select(movieSerie2, title:description)
This is readable, but can clutter up your workspace with lots of objects that you have to name individually. With multiple steps, that can be hard to keep track of.
You can also nest functions (i.e. one function inside of another), like this:
R
movieSerie_ch <- select(filter(movieSerie, age_certification == "PG-13"),
title:description)
This is handy, as R evaluates the expression from the inside out (in this case, filtering, then selecting), but it can be difficult to read if too many functions are nested,
The last option, pipes, are a recent addition to R. Pipes
let you take the output of one function and send it directly to the
next, which is useful when you need to do many things to the same
dataset. Pipes in R look like %>% and are made available
via the magrittr package, installed
automatically with dplyr. If you use
RStudio, you can type the pipe with:
- Ctrl + Shift + M if you have a PC or
Cmd + Shift + M if you have a Mac.
R
movieSerie %>%
filter(age_certification == "PG-13") %>%
select(title,description)
OUTPUT
# A tibble: 451 × 2
title description
<chr> <chr>
1 The Professionals "An arrogant Texas millionaire hires f…
2 Awakenings "Dr. Malcolm Sayer, a shy research phy…
3 National Lampoon's Christmas Vacation "It's Christmastime, and the Griswolds…
4 Lean On Me "When principal Joe Clark takes over d…
5 Mission: Impossible "When Ethan Hunt, the leader of a crac…
6 Forrest Gump "A man with a low IQ has accomplished …
7 Titanic "101-year-old Rose DeWitt Bukater tell…
8 Mission: Impossible II "With computer genius Luther Stickell …
9 Dumb and Dumber "Lloyd and Harry are two men whose stu…
10 Gattaca "In a future society in the era of ind…
# ℹ 441 more rowsIn the above code, we use the pipe to send the
movieSerie dataset first through filter() to
keep rows where age_certification is “PG-13”, then through
select() to keep only the title and
description columns. Since %>% takes the
object on its left and passes it as the first argument to the function
on its right, we don’t need to explicitly include the dataframe as an
argument to the filter() and select()
functions any more.
Some may find it helpful to read the pipe like the word “then”. For
instance, in the above example, we take the dataframe
movieSerie, then we filter for rows
with age_certification == "PG-13", then we
select columns title and
description. The dplyr
functions by themselves are somewhat simple, but by combining them into
linear workflows with the pipe, we can accomplish more complex data
wrangling operations.
If we want to create a new object with this smaller version of the data, we can assign it a new name:
R
movieSerie_ch <- movieSerie %>%
filter(age_certification == "PG-13") %>%
select(title,description)
movieSerie_ch
OUTPUT
# A tibble: 451 × 2
title description
<chr> <chr>
1 The Professionals "An arrogant Texas millionaire hires f…
2 Awakenings "Dr. Malcolm Sayer, a shy research phy…
3 National Lampoon's Christmas Vacation "It's Christmastime, and the Griswolds…
4 Lean On Me "When principal Joe Clark takes over d…
5 Mission: Impossible "When Ethan Hunt, the leader of a crac…
6 Forrest Gump "A man with a low IQ has accomplished …
7 Titanic "101-year-old Rose DeWitt Bukater tell…
8 Mission: Impossible II "With computer genius Luther Stickell …
9 Dumb and Dumber "Lloyd and Harry are two men whose stu…
10 Gattaca "In a future society in the era of ind…
# ℹ 441 more rowsNote that the final dataframe (movieSerie_ch) is the
leftmost part of this expression.
R
movieSerie %>%
filter(release_year > 1980) %>%
select(title, runtime, age_certification)
OUTPUT
# A tibble: 5,815 × 3
title runtime age_certification
<chr> <dbl> <chr>
1 Seinfeld 24 TV-PG
2 GoodFellas 145 R
3 Full Metal Jacket 117 R
4 Once Upon a Time in America 139 R
5 When Harry Met Sally... 96 R
6 A Nightmare on Elm Street 91 R
7 Steel Magnolias 119 PG
8 Police Academy 97 R
9 Christine 110 R
10 Knight Rider 51 TV-PG
# ℹ 5,805 more rowsMutate
Frequently you’ll want to create new columns based on the values in
existing columns, for example to do unit conversions, or to find the
ratio of values in two columns. For this we’ll use
mutate().
We might be interested in knowing the differences in scores on imdb vs tmdb:
R
movieSerie %>%
mutate(score_difference = imdb_score - tmdb_score) %>%
select(imdb_score, tmdb_score, score_difference)
OUTPUT
# A tibble: 5,850 × 3
imdb_score tmdb_score score_difference
<dbl> <dbl> <dbl>
1 NA NA NA
2 8.2 8.18 0.0210
3 7.7 7.3 0.400
4 8.2 7.81 0.389
5 7.7 7.6 0.100
6 8.8 8.31 0.494
7 8 7.8 0.200
8 7.7 7.5 0.200
9 7.7 7.5 0.200
10 5.8 6.16 -0.356
# ℹ 5,840 more rowsExercise
Create a new dataframe from the movieSerie data set that
meets the following criteria: contains only the title
column and a new column called total_score containing a
value that is equal to the total number of scores on both imdb and tmdb
(imdb_score plus tmdb_score). Only the rows
where total_score is greater than 15 should be shown in the
final dataframe.
Hint: think about how the commands should be ordered to produce the data frame!
R
movieSerie_total_score <- movieSerie %>%
mutate(total_score = imdb_score + tmdb_score) %>%
filter(total_score > 15) %>%
select(title, total_score)
Split-apply-combine data analysis and the summarize() function
Many data analysis tasks can be approached using the
split-apply-combine paradigm: split the data into groups, apply
some analysis to each group, and then combine the results.
dplyr makes this very easy through the use
of the group_by() function.
The summarize() function
group_by() is often used together with
summarize(), which collapses each group into a single-row
summary of that group. group_by() takes as arguments the
column names that contain the categorical variables for
which you want to calculate the summary statistics. So to compute the
average imdb_score by genre:
R
movieSerie %>%
group_by(genre) %>%
summarize(mean_imdb_score = mean(imdb_score, na.rm = TRUE))
OUTPUT
# A tibble: 19 × 2
genre mean_imdb_score
<chr> <dbl>
1 action 6.28
2 animation 6.55
3 comedy 6.33
4 crime 6.73
5 documentation 7.07
6 drama 6.73
7 family 6.21
8 fantasy 6.23
9 history 6.69
10 horror 5.45
11 music 6.62
12 reality 6.32
13 romance 6.07
14 scifi 6.69
15 sport 6.68
16 thriller 6.12
17 war 6.98
18 western 6.23
19 <NA> 7.25You may also have noticed that the output from these calls doesn’t
run off the screen anymore. It’s one of the advantages of
tbl_df over dataframe.
You can also group by multiple columns:
R
movieSerie %>%
group_by(genre, type) %>%
summarize(mean_imdb_score = mean(imdb_score, na.rm = TRUE))
OUTPUT
`summarise()` has grouped output by 'genre'. You can override using the
`.groups` argument.OUTPUT
# A tibble: 38 × 3
# Groups: genre [19]
genre type mean_imdb_score
<chr> <chr> <dbl>
1 action MOVIE 5.94
2 action SHOW 6.87
3 animation MOVIE 6.32
4 animation SHOW 6.68
5 comedy MOVIE 6.09
6 comedy SHOW 6.98
7 crime MOVIE 6.39
8 crime SHOW 7.09
9 documentation MOVIE 6.99
10 documentation SHOW 7.18
# ℹ 28 more rowsNote that the output is a grouped tibble. To obtain an ungrouped
tibble, use the ungroup function:
R
movieSerie %>%
group_by(genre, type) %>%
summarize(mean_imdb_score = mean(imdb_score, na.rm = TRUE)) %>%
ungroup()
OUTPUT
`summarise()` has grouped output by 'genre'. You can override using the
`.groups` argument.OUTPUT
# A tibble: 38 × 3
genre type mean_imdb_score
<chr> <chr> <dbl>
1 action MOVIE 5.94
2 action SHOW 6.87
3 animation MOVIE 6.32
4 animation SHOW 6.68
5 comedy MOVIE 6.09
6 comedy SHOW 6.98
7 crime MOVIE 6.39
8 crime SHOW 7.09
9 documentation MOVIE 6.99
10 documentation SHOW 7.18
# ℹ 28 more rowsOnce the data are grouped, you can also summarize multiple variables at the same time (and not necessarily on the same variable). For instance, we could add a column indicating the maximum imdb_score given to a movie or serie:
R
movieSerie %>%
group_by(genre, type) %>%
summarize(mean_imdb_score = mean(imdb_score, na.rm = TRUE),
max_imdb_score = max(imdb_score, na.rm = TRUE))
OUTPUT
`summarise()` has grouped output by 'genre'. You can override using the
`.groups` argument.OUTPUT
# A tibble: 38 × 4
# Groups: genre [19]
genre type mean_imdb_score max_imdb_score
<chr> <chr> <dbl> <dbl>
1 action MOVIE 5.94 9.1
2 action SHOW 6.87 9
3 animation MOVIE 6.32 9.1
4 animation SHOW 6.68 9
5 comedy MOVIE 6.09 8.7
6 comedy SHOW 6.98 9.2
7 crime MOVIE 6.39 8.6
8 crime SHOW 7.09 8.8
9 documentation MOVIE 6.99 8.9
10 documentation SHOW 7.18 9.3
# ℹ 28 more rowsIt is sometimes useful to rearrange the result of a query to inspect
the values. For instance, we can sort on min_imdb_score to
put the group with the smallest imdb_score first:
R
movieSerie %>%
group_by(genre, type) %>%
summarize(mean_imdb_score = mean(imdb_score, na.rm = TRUE),
max_imdb_score = max(imdb_score, na.rm = TRUE)) %>%
arrange(max_imdb_score)
OUTPUT
`summarise()` has grouped output by 'genre'. You can override using the
`.groups` argument.OUTPUT
# A tibble: 38 × 4
# Groups: genre [19]
genre type mean_imdb_score max_imdb_score
<chr> <chr> <dbl> <dbl>
1 music SHOW 6.3 6.9
2 horror SHOW 6.19 7
3 sport MOVIE 6.27 7.4
4 history MOVIE 6.43 7.5
5 reality MOVIE 7.15 7.5
6 western SHOW 7.45 7.6
7 family MOVIE 5.81 7.7
8 fantasy SHOW 6.87 7.7
9 <NA> MOVIE 7.1 7.7
10 sport SHOW 7.9 7.9
# ℹ 28 more rowsTo sort in descending order, we need to add the desc()
function. If we want to sort the results by decreasing order of minimum
imdb_score:
R
movieSerie %>%
group_by(genre, type) %>%
summarize(mean_imdb_score = mean(imdb_score, na.rm = TRUE),
max_imdb_score = max(imdb_score, na.rm = TRUE)) %>%
arrange(desc(max_imdb_score))
OUTPUT
`summarise()` has grouped output by 'genre'. You can override using the
`.groups` argument.OUTPUT
# A tibble: 38 × 4
# Groups: genre [19]
genre type mean_imdb_score max_imdb_score
<chr> <chr> <dbl> <dbl>
1 <NA> SHOW 7.32 9.6
2 drama SHOW 7.19 9.5
3 reality SHOW 6.31 9.5
4 documentation SHOW 7.18 9.3
5 scifi SHOW 7.08 9.3
6 comedy SHOW 6.98 9.2
7 action MOVIE 5.94 9.1
8 animation MOVIE 6.32 9.1
9 action SHOW 6.87 9
10 animation SHOW 6.68 9
# ℹ 28 more rowsCounting
When working with data, we often want to know the number of
observations found for each factor or combination of factors. For this
task, dplyr provides count().
For example, if we wanted to count the number of rows of data for each
village, we would do:
R
movieSerie %>%
count(release_year)
OUTPUT
# A tibble: 63 × 2
release_year n
<dbl> <int>
1 1945 1
2 1954 2
3 1956 1
4 1958 1
5 1959 1
6 1960 1
7 1961 1
8 1963 1
9 1966 1
10 1967 2
# ℹ 53 more rowsFor convenience, count() provides the sort
argument to get results in decreasing order:
R
movieSerie %>%
count(release_year, sort = TRUE)
OUTPUT
# A tibble: 63 × 2
release_year n
<dbl> <int>
1 2019 836
2 2020 814
3 2021 787
4 2018 773
5 2017 563
6 2022 371
7 2016 362
8 2015 223
9 2014 153
10 2013 135
# ℹ 53 more rowsR
movieSerie %>%
count(age_certification)
OUTPUT
# A tibble: 12 × 2
age_certification n
<chr> <int>
1 "" 2619
2 "G" 124
3 "NC-17" 16
4 "PG" 233
5 "PG-13" 451
6 "R" 556
7 "TV-14" 474
8 "TV-G" 79
9 "TV-MA" 883
10 "TV-PG" 188
11 "TV-Y" 107
12 "TV-Y7" 120R
movieSerie %>%
group_by(genre) %>%
summarize(
mean_tmdb_score = mean(tmdb_score, na.rm = TRUE),
min_tmdb_score = min(tmdb_score, na.rm = TRUE),
max_tmdb_score = max(tmdb_score, na.rm = TRUE),
n = n()
)
OUTPUT
# A tibble: 19 × 5
genre mean_tmdb_score min_tmdb_score max_tmdb_score n
<chr> <dbl> <dbl> <dbl> <int>
1 action 6.75 2 10 365
2 animation 7.31 2 10 317
3 comedy 6.59 1 10 1305
4 crime 6.92 3.8 10 238
5 documentation 7.11 1 10 665
6 drama 6.96 1 10 1421
7 family 7.14 1 10 113
8 fantasy 6.77 2 10 88
9 history 6.94 5.8 10 21
10 horror 5.83 2.8 8.5 114
11 music 7.09 5.3 8.8 59
12 reality 7.19 1 10 171
13 romance 6.42 2 9.3 232
14 scifi 7.17 0.5 9.5 239
15 sport 6.8 5 8.3 4
16 thriller 6.39 3.7 10 377
17 war 6.93 4.8 8.8 46
18 western 6.30 3.6 8.15 16
19 <NA> 7.06 1 10 59Exporting data
Now that you have learned how to use
dplyr to extract information from or
summarize your raw data, you may want to export these new data sets to
share them with your collaborators or for archival.
Similar to the read_csv() function used for reading CSV
files into R, there is a write_csv() function that
generates CSV files from dataframes.
Before using write_csv(), we are going to create a new
folder, data_output, in our working directory that will
store this generated dataset. We don’t want to write generated datasets
in the same directory as our raw data. It’s good practice to keep them
separate. The data folder should only contain the raw,
unaltered data, and should be left alone to make sure we don’t delete or
modify it. In contrast, our script will generate the contents of the
data_output directory, so even if the files it contains are
deleted, we can always re-generate them.
Now we can save this dataframe to our data_output
directory.
R
write_csv(movieSerie_ch, file = "data_output/movieSerie_changed.csv")
Key Points
- Use the
dplyrpackage to manipulate dataframes. - Use
select()to choose variables from a dataframe. - Use
filter()to choose data based on values. - Use
group_by()andsummarize()to work with subsets of data. - Use
mutate()to create new variables. - Use the
tidyrpackage to change the layout of dataframes. - Use
pivot_wider()to go from long to wide format. - Use
pivot_longer()to go from wide to long format.