awk NR==FNR output control Post: 302532027

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Top Forums UNIX for Dummies Questions & Answers awk NR==FNR output control Post 302532027 by agama on Sunday 19th of June 2011 11:06:04 AM

06-19-2011

Registered User

The short answer is to process f2 first, then process f1. This will reduce your memory footprint as you'll only save 68 things in a[] rather than 48K things.

The long answer is to be a bit more clever which might also help speed things up. Your programme will loop through the entire contents of file f1 for each record in f2 (48,000 * 68) testing to see if there's a match. Instead, use the hash capabilities of awk to your advantage.

This example assumes that the 'key' (field 1 in file 2) can occur multiple times and so we must do a bit of looping for each f1 record, but the only looping needed when reading limited to the number of duplicate 'keys' that existed in f2 for the current f1 record. If f2 will not have duplicates, then the code can be simplified more, but not knowing you exact data, this general case will work for either. We also don't need to make an explicit check to see if the key in the current record matches the one saved from f2.

Code:

awk -v f2=f2 '
    BEGIN {
        while( (getline<f2) > 0 )   # read and collect records from f2
        {
            key = $1;
            ki = kidx[key]++;        # track number of duplicate keys (0 based)
            k2rec[key,ki] = $0;      # save unique record by key and dup count
        }
        close( f2 );
    }

    {
        key = $3;
        for( i = 0; i < kidx[key]; i++ )          # for each duplicate of key
            printf( "%s\t%s\n", k2rec[key,i], $0 );   # print f2 record, followed by current f1 record
    }
' <f1 >f3

Hope this makes sense.

Last edited by agama; 06-19-2011 at 12:07 PM.. Reason: Corrected printf to output f2 then f1

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igawk

IGAWK(1)							 Utility Commands							  IGAWK(1)

NAME

       igawk - gawk with include files

SYNOPSIS

       igawk [ all gawk options ] -f program-file [ -- ] file ...
       igawk [ all gawk options ] [ -- ] program-text file ...

DESCRIPTION

       Igawk is a simple shell script that adds the ability to have ``include files'' to gawk(1).

       AWK programs for igawk are the same as for gawk, except that, in addition, you may have lines like

	      @include getopt.awk

       in your program to include the file getopt.awk from either the current directory or one of the other directories in the search path.

OPTIONS

       See gawk(1) for a full description of the AWK language and the options that gawk supports.

EXAMPLES

       cat << EOF > test.awk
       @include getopt.awk

       BEGIN {
	    while (getopt(ARGC, ARGV, "am:q") != -1)
		 ...
       }
       EOF

       igawk -f test.awk

SEE ALSO

       gawk(1)

       Effective AWK Programming, Edition 1.0, published by the Free Software Foundation, 1995.

AUTHOR

       Arnold Robbins (arnold@skeeve.com).

Free Software Foundation					    Nov 3 1999								  IGAWK(1)

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