13.9 transpose - Perform a Matrix Transposition

Contributed by Geoff Clare

transpose performs a matrix transposition on its input. I wrote this when I saw a script to do this job posted to the Net and thought it was horribly inefficient. I posted mine as an alternative with timing comparisons. If I remember rightly, the original one stored all the elements individually and used a nested loop with a printf for each element. It was immediately obvious to me that it would be much faster to construct the rows of the transposed matrix "on the fly."

My script uses ${1+"$@ " } to supply file names on the awk command line so that if no files are specified awk will read its standard input. This is much better than plain $* which can't handle filenames containing whitexspace.

#! /bin/sh # Transpose a matrix: assumes all lines have same number # of fields  exec awk ' NR == 1 { 	n = NF 	for (i = 1; i <= NF; i++) 		row[i] = $i 	next } { 	if (NF > n) 		n = NF 	for (i = 1; i <= NF; i++) 		row[i] = row[i] " " $i } END { 	for (i = 1; i <= n; i++) 		print row[i] }' ${1+"$@"}

Here's a test file:

1 2 3 4 5 6 7 8 9 10 11 12

Now we run transpose on the file.

$ 

transpose test

 1 5 9 2 6 10 3 7 11 4 8 12