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In a huge file, Delete duplicate lines leaving unique lines

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# 15  
Old 08-02-2011
Originally Posted by yazu
Because this is O(n^2) algorithm. And for 4GB file it will work really very long. (Days, months? Who knows... Smilie )
Also because it's a frequent shell mistake which attempts to load the entire thing into memory at once. Whatever the limit for shell variables on your system is, it's probably less than 40 gigabytes!
# 16  
Old 08-02-2011
Originally Posted by yazu
You can split the file (with "split" command), then "sort -u" the chunks separately and then merge them with "sort -m". (Of course whether you need it depends on the memory size of your system).
You probably won't have to split anything manually. Many (if not most) sort implementations (GNU, *BSD, Solaris, HP-UX, to name a few) will do this for you automatically. They compare the size of the file to be sorted against the system's available memory and make a conservative guess. Intermediate files are then created in $TMPDIR.

As vgersh99 pointed out, often there'll be a -T option to override the enviroment variable, although if this option is missing, you can simply override the environment default when invoking sort (TMPDIR=/lots/of/space sort ...).

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# 17  
Old 08-04-2011
Thank you everyone.

I am using awk '!($0 in a){a[$0];print}' which I found efficient out of all options.

Last edited by radoulov; 08-04-2011 at 05:51 AM.. Reason: Code tags.

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