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 <- data.frame(var1 = c(0, NA, 2, 2, 5), var2 = c(5, 5, 7, 8, 9), var3 = c(2, 7, 9, 9, 7)) #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 namedrow_sumdata$row_sum <- rowSums(data[ , c(1,3)], na.rm=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 <- rowSums(data, na.rm=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.*