How to aggregate multiple columns in a dataframe in R?
This recipe helps you aggregate multiple columns in a dataframe in R
Recipe Objective
Aggregate function is used in similar places where to apply function is applied. It calculates the summary statistics after collating raw data with respect to a grouping variable in a dataset.
It is a two step process. Firstly, it groups the raw data based on a categorical variable and then perform the required calculation on each groups formed.
There are three things which is required to perform aggregation: Data, grouping variable and function/calculation to perform.
Syntax: aggregate (x, by = , FUN = )
Where:
- x = dataframe
- by = Grouping variable/column in the form of list input
- FUN = built-in or derived function that needs to be performed on multiple columns after aggregation.
In this recipe, we will demonstrate how to aggregate multiple columns in a dataframe in R.
Table of Contents
Step 1: Creating a DataFrame
Creating a STUDENT dataframe with Name and marks of two subjects in 3 Trimester exams.
STUDENT = data.frame(Name = c("Ram","Ram", "Ram", "Shyam", "Shyam", "Shyam", "Jessica", "Jessica", "Jessica"),
Science_Marks = c(55, 60, 65, 80, 70, 75, 45, 65, 70),
Math_Marks = c(70, 75, 73, 50, 53, 55, 65, 78, 75),
Trimester = c(1, 2, 3, 1, 2, 3, 1, 2, 3))
STUDENT
Name Science_Marks Math_Marks Trimester
Ram 55 70 1
Ram 60 75 2
Ram 65 73 3
Shyam 80 50 1
Shyam 70 53 2
Shyam 75 55 3
Jessica 45 65 1
Jessica 65 78 2
Jessica 70 75 3
Step 2: Application of Aggregate Function
Query 1: To find the average marks for each student in a year (Trimester 1, 2 and 3)
We will use aggregate function to carry out this task with grouping variable as "Name" and FUN = mean.
aggregate(STUDENT[ , 2:3], by = list(STUDENT$Name), FUN = mean)
Group_1 Science_Marks Math_Marks
Jessica 60 72.66667
Ram 60 72.66667
Shyam 75 52.66667
Query 2: To find the average marks of the subjects in each trimester.
We will use aggregate function to carry out this task with grouping variable as "Trimester" and FUN = mean.
aggregate(STUDENT[ , 2:3], by = list(STUDENT$Trimester), FUN = mean)
Group_1 Science_Marks Math_Marks
1 60 61.66667
2 65 68.66667
3 70 67.66667
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Abhinav Agarwal
I come from Northwestern University, which is ranked 9th in the US. Although the high-quality academics at school taught me all the basics I needed, obtaining practical experience was a challenge.... Read More