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In R, it is possible to aggregate multiple columns using the aggregate() function, which works in a similar way to the lapply() and apply() functions. The aggregate() function requires three arguments: an object (e.g. a data frame) to be aggregated, a formula that specifies which columns to aggregate, and a function to be applied to each group of columns. This allows the user to easily group and summarise data according to multiple columns.
We can use the aggregate() function in R to produce summary statistics for one or more variables in a data frame.
This function uses the following basic syntax:
aggregate(sum_var ~ group_var, data = df, FUN = mean)
where:
- sum_var: The variable to summarize
- group_var: The variable to group by
- data: The name of the data frame
- FUN: The summary statistic to compute
This tutorial provides several examples of how to use this function to aggregate one or more columns at once in R, using the following data frame as an example:
#create data frame df <- data.frame(team=c('A', 'A', 'A', 'B', 'B', 'B', 'C', 'C'), conf=c('E', 'E', 'W', 'W', 'W', 'W', 'W', 'W'), points=c(1, 3, 3, 4, 5, 7, 7, 9), rebounds=c(7, 7, 8, 3, 2, 7, 14, 13)) #view data frame df team conf points rebounds 1 A E 1 7 2 A E 3 7 3 A W 3 8 4 B W 4 3 5 B W 5 2 6 B W 7 7 7 C W 7 14 8 C W 9 13
Example 1: Summarize One Variable & Group by One Variable
The following code shows how to find the mean points scored, grouped by team:
#find mean points scored, grouped by team aggregate(points ~ team, data = df, FUN = mean, na.rm = TRUE) team points 1 A 2.333333 2 B 5.333333 3 C 8.000000
Example 2: Summarize One Variable & Group by Multiple Variables
The following code shows how to find the mean points scored, grouped by team and conference:
#find mean points scored, grouped by team and conference aggregate(points ~ team + conf, data = df, FUN = mean, na.rm = TRUE) team conf points 1 A E 2.000000 2 A W 3.000000 3 B W 5.333333 4 C W 8.000000
Example 3: Summarize Multiple Variables & Group by One Variable
The following code shows how to find the mean points and the mean rebounds, grouped by team:
#find mean points scored, grouped by team and conference aggregate(cbind(points,rebounds) ~ team, data = df, FUN = mean, na.rm = TRUE) team points rebounds 1 A 2.333333 7.333333 2 B 5.333333 4.000000 3 C 8.000000 13.500000
Example 4: Summarize Multiple Variables & Group by Multiple Variables
#find mean points scored, grouped by team and conference aggregate(cbind(points,rebounds) ~ team + conf, data = df, FUN = mean, na.rm = TRUE) team conf points rebounds 1 A E 2.000000 7.0 2 A W 3.000000 8.0 3 B W 5.333333 4.0 4 C W 8.000000 13.5