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 #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 #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