How can I stack columns per x columns in R

Question

I\'m looking to transform a data frame of 660 columns into 3 columns just by stacking them on each other per 3 columns without manually re-arranging (since I have 660 column

Answer 1

rbind.data.frame requires that all columns match up. So use setNames to replace the names of the C:D columns:

rbind( dat[1:2], setNames(dat[3:4], names(dat[1:2]))  )
  A  B
1 1  4
2 2  5
3 3  6
4 7 10
5 8 11
6 9 12

To generalize that to multiple columns use do.call and lapply:

 dat <- setNames( as.data.frame( matrix(1:36, ncol=12) ), LETTERS[1:12])
 dat
#----
  A B C  D  E  F  G  H  I  J  K  L
1 1 4 7 10 13 16 19 22 25 28 31 34
2 2 5 8 11 14 17 20 23 26 29 32 35
3 3 6 9 12 15 18 21 24 27 30 33 36


do.call( rbind, lapply( seq(1,12, by=3), function(x) setNames(dat[x:(x+2)], LETTERS[1:3])   ))
    A  B  C
1   1  4  7
2   2  5  8
3   3  6  9
4  10 13 16
5  11 14 17
6  12 15 18
7  19 22 25
8  20 23 26
9  21 24 27
10 28 31 34
11 29 32 35
12 30 33 36

The 12 would be replaced by 660 and everything else should work.