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Often you may want to find the sum of a specific set of columns in a data frame in R. Fortunately this is easy to do using the rowSums() function.
This tutorial shows several examples of how to use this function in practice.
Example 1: Find the Sum of Specific Columns
The following code shows how to create a data frame with three columns and find the sum of the first and third columns:
#create data frame data #view data frame data var1 var2 var3 1 0 5 2 2 NA 5 7 3 2 7 9 4 2 8 9 5 5 9 7 #find sum of first and third columns rowSums(data[ , c(1,3)], na.rm=TRUE) [1] 2 7 11 11 12
The way to interpret the output is as follows:
- The sum of values in the first row for the first and third columns is 2.
- The sum of values in the first row for the first and third columns is 7.
- The sum of values in the first row for the first and third columns is 11.
- The sum of values in the first row for the first and third columns is 11.
- The sum of values in the first row for the first and third columns is 12.
You can also assign the row sums of these specific columns to a new variable in the data frame:
#assign row sums to new variable named row_sum data$row_sum TRUE) #view data frame data var1 var2 var3 row_sum 1 0 5 2 2 2 NA 5 7 7 3 2 7 9 11 4 2 8 9 11 5 5 9 7 12
Example 2: Find the Sum of All Columns
It’s also possible to find the sum across all columns in a data frame. The following code shows how to do so:
#find row sums across all columns data$new TRUE) #view data frame data var1 var2 var3 new 1 0 5 2 7 2 NA 5 7 12 3 2 7 9 18 4 2 8 9 19 5 5 9 7 21
We can see that:
- The sum of values in the first row across all three columns is 7.
- The sum of values in the second row across all three columns is 12.
And so on.
You can find more R tutorials here.