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Top Forums UNIX for Advanced & Expert Users Performance problem with removing duplicates in a huge file (50+ GB) Post 302751861 by DGPickett on Friday 4th of January 2013 03:46:13 PM
Old 01-04-2013
The sort -u has less scaling difficulty than associative arrays in a shell. If the order of lines is important, number them first, then sort out the duplicates, then sort it back to original order and then remove numbering. The sort will save the first of any duplicates.

JAVA and C++ PPIs like RogueWave H++ have the same associative array functionality, more accurately called a hash map container. The file could be mmap64() mapped to the program so the hash map just has hash keys and offsets. The clean file could be recreated or even updated in place and truncated with fcntl(). The shell has noticably more overhead. Big jobs often need sharper tools.

Last edited by DGPickett; 01-04-2013 at 04:53 PM..
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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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