Often you may want to stack two or more data frame columns into one column in R.

For example, you may want to go from this:

person trial outcome1 outcome2 A 1 7 4 A 2 6 4 B 1 6 5 B 2 5 5 C 1 4 3 C 2 4 2

To this:

person trial outcomes value A 1 outcome1 7 A 2 outcome1 6 B 1 outcome1 6 B 2 outcome1 5 C 1 outcome1 4 C 2 outcome1 4 A 1 outcome2 4 A 2 outcome2 4 B 1 outcome2 5 B 2 outcome2 5 C 1 outcome2 3 C 2 outcome2 2

This tutorial explains two methods you can use in R to do this.

**Method 1: Use the Stack Function in Base R**

The following code shows how to stack columns using the **stack **function in base R:

#create original data frame data <- data.frame(person=c('A', 'A', 'B', 'B', 'C', 'C'), trial=c(1, 2, 1, 2, 1, 2), outcome1=c(7, 6, 6, 5, 4, 4), outcome2=c(4, 4, 5, 5, 3, 2)) #stack the third and fourth columns cbind(data[1:2], stack(data[3:4])) person trial values ind 1 A 1 7 outcome1 2 A 2 6 outcome1 3 B 1 6 outcome1 4 B 2 5 outcome1 5 C 1 4 outcome1 6 C 2 4 outcome1 7 A 1 4 outcome2 8 A 2 4 outcome2 9 B 1 5 outcome2 10 B 2 5 outcome2 11 C 1 3 outcome2 12 C 2 2 outcome2

**Method 2: Use the Melt Function from Reshape2**

The following code shows how to stack columns using the **melt **function from the **reshape2 **library:

#load library library(reshape2) #create original data frame data <- data.frame(person=c('A', 'A', 'B', 'B', 'C', 'C'), trial=c(1, 2, 1, 2, 1, 2), outcome1=c(7, 6, 6, 5, 4, 4), outcome2=c(4, 4, 5, 5, 3, 2)) #melt columns of data frame melt(data, id.var = c('person', 'trial'), variable.name = 'outcomes') person trial outcomes value 1 A 1 outcome1 7 2 A 2 outcome1 6 3 B 1 outcome1 6 4 B 2 outcome1 5 5 C 1 outcome1 4 6 C 2 outcome1 4 7 A 1 outcome2 4 8 A 2 outcome2 4 9 B 1 outcome2 5 10 B 2 outcome2 5 11 C 1 outcome2 3 12 C 2 outcome2 2

*You can find the complete documentation for the melt function here.*

**Additional Resources**

How to Switch Two Columns in R

How to Rename Columns in R

How to Sum Specific Columns in R