R: unexpected `ifelse` behavior

I have a data frame like the following:

mydf <- data.frame(letter=LETTERS[1:10],
                   val1=sample(1:1000, 10, replace=F),
                   val2=sample(1:1000, 10, replace=F))
> mydf
   letter val1 val2
1       A  877  250
2       B  554  427
3       C  747   92
4       D  353  890
5       E  957  194
6       F  593  338
7       G  723  731
8       H  218  849
9       I  585  932
10      J  873  642

I just want to make a new column which (for this MWE) is equal to one of the value columns, depending on a choose variable, and I wanted to use ifelse for this purpose.

I do this:

  choose <- 1
  mydf$chosen <- ifelse(choose==1, mydf$val1, mydf$val2)
  mydf

But it just uses the first value of val1 for the chosen column... what am I doing wrong here? Thanks

> mydf
   letter val1 val2 chosen
1       A  878  984    878
2       B  880   80    878
3       C  296  999    878
4       D  558  230    878
5       E  112  414    878
6       F  132  450    878
7       G  429  693    878
8       H  608   89    878
9       I  409   50    878
10      J  974  980    878