You can use the following syntax to calculate a percentage by group in R:
library(dplyr)
df %>%
group_by(group_var) %>%
mutate(percent = value_var/sum(value_var))
The following example shows how to use this syntax in practice.
Example: Calculate Percentage by Group in R
Suppose we have the following data frame that shows the points scored by basketball players on various teams:
#create data frame
df <- data.frame(team=c('A', 'A', 'A', 'A', 'A', 'B', 'B', 'B', 'B', 'B'),
points=c(12, 29, 34, 14, 10, 11, 7, 36, 34, 22))
#view data frame
df
team points
1 A 12
2 A 29
3 A 34
4 A 14
5 A 10
6 B 11
7 B 7
8 B 36
9 B 34
10 B 22
We can use the following code to create a new column in the data frame that shows the percentage of total points scored, grouped by team:
library(dplyr) #calculate percentage of points scored, grouped by team df %>% group_by(team) %>% mutate(percent = points/sum(points)) # A tibble: 10 x 3 # Groups: team [2] team points percent 1 A 12 0.121 2 A 29 0.293 3 A 34 0.343 4 A 14 0.141 5 A 10 0.101 6 B 11 0.1 7 B 7 0.0636 8 B 36 0.327 9 B 34 0.309 10 B 22 0.2
The percent column shows the percentage of total points scored by that player within their team.
For example, players on team A scored a total of 99 points.
Thus, the player in the first row of the data frame who scored 12 points scored a total of 12/99 = 12.12% of the total points for team A.
Similarly, the player in the second row of the data frame who scored 29 points scored a total of 29/99 = 29.29% of the total points for team A.
And so on.
Additional Resources
The following tutorials explain how to perform other common tasks in R:
How to Count Unique Values by Group in R
How to Calculate Summary Statistics by Group in R
How to Calculate the Sum by Group in R
