uniq: group similar lines

[Jérémy Compostella]

All,

I'm interested to work on the uniq --group feature as described in the
following thread:
http://lists.gnu.org/archive/html/coreutils/2011-03/msg00000.html

$ printf "1 a\n2 a\n2 b\n3 a\n3 b\n4 a\n" | uniq -w1 --group
1 a

2 a
2 b

3 a
3 b

4 a

With this new option, uniq becomes very useful to easily separate block
of similar lines in a file. --group would be an addition to modify the
default behavior : instead of suppress similar lines, separate block of
similar lines.

I do not agree with the proposition of using the --group option in
conjunction with the -u option or with the -D option for the following
reasons:

1. -D, --all-repeated already has the appropriate argument : "separate".
2. -u, --unique could be enhance with the same kind of arguments than
   --all-repeated.
3. Above all, IMHO, --group option would be an addition to provide a new
   behavior and not a new way to access an already existing behavior.

Maybe, we could consider the --unique=[delimit-method] addition too
although it seems less interesting and I do not see any use case.

What do you think ?

Cheers,

Jérémy
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