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Full Discussion: Merging columns based on one or more column in two files
Top Forums Shell Programming and Scripting Merging columns based on one or more column in two files Post 302694501 by agama on Thursday 30th of August 2012 10:31:51 PM
Old 08-30-2012
If file one isn't too large, then this should work

Code:
# single pass across each file, but requires the entire first file
# to be held in memory which might not be realistic.
# order is preserved based on file2
awk '
    NR == FNR { cache[$1] = $0; next; }
    $1 in cache {
        printf( "%s", cache[$1] );
        $1 = "";
        print;
    }
' file1 file2 >output

If file1 is large (i.e. it's not practical to cache it in memory), then this is one way. May not be the most efficent, but it should work. The order of the output is sorted by field1.

Code:
# multiple passes across the data, but memory requirement is eliminated
# order of file2 is not preserved.
(
    sed 's/^/a /' file1
    sed 's/^/b /' file2
) | sort -k 2n,2 -k 1,1  awk '
    $1 == "a" {
        x = $2;
        $1 = "";
        cache = $0;
        next;
    }
    $2 == x {
        $1 = $2 ="";
        printf( "%s%s\n", substr( cache, 2 ), $0 );
    }
'

You could do this without the seds, and depend on the number of columns to determine if an unmatched pair exists, but this works without having to know the exact layout of either file, other than the desired column to compare.

Yes, multiple columns can be used to match.
Last edited by agama; 08-30-2012 at 11:38 PM.. Reason: small efficiency change.
 

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LEARN ABOUT SUSE

xzcmp

XZDIFF(1)							     XZ Utils								 XZDIFF(1)

NAME

       xzcmp, xzdiff, lzcmp, lzdiff - compare compressed files

SYNOPSIS

       xzcmp [cmp_options] file1 [file2]
       xzdiff [diff_options] file1 [file2]
       lzcmp [cmp_options] file1 [file2]
       lzdiff [diff_options] file1 [file2]

DESCRIPTION

       xzcmp  and  xdiff invoke cmp(1) or diff(1) on files compressed with xz(1), lzma(1), gzip(1), or bzip2(1).  All options specified are passed
       directly to cmp or diff.  If only one file is specified, then the files compared are file1 (which must have a suffix of	a  supported  com-
       pression  format)  and  file1 from which the compression format suffix has been stripped.  If two files are specified, then they are uncom-
       pressed if necessary and fed to cmp(1) or diff(1).  The exit status from cmp or diff is preserved.

       The names lzcmp and lzdiff are provided for backward compatibility with LZMA Utils.

SEE ALSO

       cmp(1), diff(1), xz(1), gzip(1), bzip2(1), zdiff(1)

BUGS

       Messages from the cmp(1) or diff(1) programs refer to temporary filenames instead of those specified.

Tukaani 							    2009-07-05								 XZDIFF(1)
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