Re: RFC: improved support for grouping in uniq

[Eric Blake]

On 03/02/2011 09:44 AM, Pádraig Brady wrote:
> -d, -D and -u make sense when used in isolation:
> 
> $ printf "1 a\n2 a\n2 b\n2 c\n3 a\n" | uniq -w1 -D
> 2 a
> 2 b
> 2 c
> $ printf "1 a\n2 a\n2 b\n2 c\n3 a\n" | uniq -w1 -u
> 1 a
> 3 a
> pb-laptop:~$ printf "1 a\n2 a\n2 b\n2 c\n3 a\n" | uniq -w1 -d
> 2 a
> 
> However when you combine -u (suppress last output entry
> in a repeated group) with -d or -D it doesn't seem useful:
> 
> $ printf "1 a\n2 a\n2 b\n2 c\n3 a\n" | uniq -w1 -d -u

This behavior is required by POSIX (-d suppresses unique lines, -u
suppresses duplicate lines, so all lines are suppressed).

> $ printf "1 a\n2 a\n2 b\n2 c\n3 a\n" | uniq -w1 -D -u
> 2 a
> 2 b

-D is a GNU invention, so we are free to make it more useful.

> 
> Why I'm asking is to perhaps overload -u -D
> to support grouping like:
> 
> $ printf "1 a\n2 a\n2 b\n2 c\n3 a\n" |
>   uniq -w1 --unique=separated --all-repeated=separated
> 1 a
> 
> 2 a
> 2 b
> 2 c
> 
> 3 a
> 
> 
> Or maybe we should just add a new --group option to do the above?

A --group option sounds interesting, even in combination with the others:

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

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

3 a
3 b
$ 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

-- 
Eric Blake   address@hidden    +1-801-349-2682
Libvirt virtualization library http://libvirt.org

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