I can't decide if this is a bug or not. Apologies if this has already been discussed I am pretty new to the list. I'm using the latest git version, 8.5.136-6d78c.
If you do
sort -R -k 4,4 a > b
the relative ordering of column 4 is different then if you do
sort -R -k 4,5 a > b.
(obviously the actual order in the output file is different on every run unless you pass in the same random data to get the same ordering)
It'd seem that the individual columns should be hashed and sorted independently in order to maintain the normal ordering of the primary sort column. It appears that the sort is on the hash of concatenated key list, so the same values of the primary sort column do not appear next to each other when sorting on multiple columns. e.g., if have an input file called "a":
a b c d e a b c d f a b c d g a b c e e a b c e f
The output file should always contain all the "a b c d" lines contiguously, and all the "a b c e" lines contiguously. As it is, the output might be
~/coreutils/coreutils> src/sort -R -k 4,5 a a b c d e a b c d g a b c e e a b c e f a b c d f