bugGNU Core Utilities - Bugs: bug #20883, sort -u -n drops more lines than...

 
 

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bug #20883: sort -u -n drops more lines than expected

Submitter:  None
Submitted:  Fri 24 Aug 2007 05:52:13 AM UTC
   
 
Category:  None Severity:  3 - Normal
Item Group:  None Status:  None
Privacy:  Public Assigned to:  rwp
Open/Closed:  Closed

Fri 24 Aug 2007 07:32:13 AM UTC, comment #1: 

Thanks for the report but this is not a bug but simply a misunderstanding of what sort is using as a sort key.  Note that since this is an anonymous bug posting I cannot respond other than by posting a response to the bug.

By default sort will consider the entire line as the sort key.  When using the -n numeric sort flag this is still true.  The reason sort -u is collapsing lines is because the sort key cause sort to believe the lines are equivalent.  Unless -k is specified to restrict the sort key the default key is the entire line.

The way to sort that input numerically on two different fields is to use the -k option to select both fields.  Try this:

  sort -k1,1n -k2,2n -u
  1 1
  1 2
  1 3
  2 1
  3 1

That will provide the result that you are looking to achieve.

Bob Proulx <rwp>
Group administrator
Fri 24 Aug 2007 05:52:13 AM UTC, original submission:  

Given the following example input:

1       3
2       1
1       1
3       1
1       2
1       1

sort -u gives the expected output:

1       1
1       2
1       3
2       1
3       1

But sort -n -u drops all lines that match the sort column:

1       3
2       1
3       1

Or compare sort -n -u -k2:

2       1
1       2
1       3

It's not clear from the info page that this is the correct behavior, but I would expect sort -n -u to do the same as sort -n  | uniq, or for this omitting equal keys (instead of equal lines) to be more explicit in the documentation.

Anonymous

 

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    Date Changed by Updated Field Previous Value => Replaced by
    2007-08-24 rwp Assigned toNone rwp
        Open/ClosedOpen Closed

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