ifelse() not storing values properly in R

I'm trying to run this code for a for loop:

ifelse(split[[1]]$timeframe == 'post',
       split[[1]]$prcntgwk <- 1,
       split[[1]]$prcntgwk <- 2)

It basically is creating a calculation unless the value of column timeframe is 'post', then it will store an NA since the calculation is not applicable

This is my output:

> ifelse(split[[1]]$timeframe == 'post',
+        split[[1]]$prcntgwk <- 1,
+        split[[1]]$prcntgwk <- 2)
[1] 2 2 2 2 2 2 2 1

But then when I retrieve the column I get this:

> split[[1]]$prcntgwk
[1] 2 2 2 2 2 2 2 2

Why aren't my values being stored properly??? This makes absolutely no sense at all.