uniq - check specific fields

[Assaf Gordon]

Hello,

Attached is a proof-of-concept patch to add "--check-fields=N" to uniq, 
allowing uniq'ing by specific fields.
(Trying a different approach at promoting csplit-by-field [1] :) ).

It works just like 'check-chars' but on fields, and if not used, it does not 
affect the program flow.
===
    # input file, every whole-line is uniq
    $ cat input.txt 
    A 1 z
    A 1 y
    A 2 x
    B 2 w
    B 3 w
    C 3 w
    C 4 w
    
    # regular uniq
    $ uniq -c input.txt 
          1 A 1 z
          1 A 1 y
          1 A 2 x
          1 B 2 w
          1 B 3 w
          1 C 3 w
          1 C 4 w
          
    # Stop after 1 field
    $ uniq -c --check-fields 1 input.txt 
          3 A 1 z
          2 B 2 w
          2 C 3 w
    
    # Stop after 2 fields
    $ uniq -c --check-fields 2 input.txt 
          2 A 1 z
          1 A 2 x
          1 B 2 w
          1 B 3 w
          1 C 3 w
          1 C 4 w
    
    # Skip the first field and check 1 field (effectively, uniq on field 2)
    $ uniq -c  --skip-fields 1 --check-fields 1 input.txt 
          2 A 1 z
          2 A 2 x
          2 B 3 w
          1 C 4 w
    
    # "--field" is convenience shortcut for skip&check fields 
    $ uniq -c --field 2 input.txt 
          2 A 1 z
          2 A 2 x
          2 B 3 w
          1 C 4 w
    $ uniq -c --field 3 input.txt 
          1 A 1 z
          1 A 1 y
          1 A 2 x
          4 B 2 w
===

What do you think ?

 -gordon

[1] http://lists.gnu.org/archive/html/coreutils/2013-02/msg00015.html

0001-uniq-support-uniq-by-field.patch
Description: Text Data