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Remove duplicate rows of an un-sorted file based on a single column

Terminal - Remove duplicate rows of an un-sorted file based on a single column
awk '{ if ($1 in stored_lines) x=1; else print; stored_lines[$1]=1 }' infile.txt > outfile.txt
2010-12-15 17:08:47
User: dopeman
Functions: awk
4
Remove duplicate rows of an un-sorted file based on a single column

The command (above) will remove any duplicate rows based on the FIRST column of data in an un-sorted file.

The '$1' represents a positional parameter. You can change both instances of '$1' in the command to remove duplicates based on a different column, for instance, the third:

awk '{ if ($3 in stored_lines) x=1; else print; stored_lines[$3]=1 }' infile.txt > outfile.txt

Or you can change it to '$0' to base the removal on the whole row:

awk '{ if ($0 in stored_lines) x=1; else print; stored_lines[$0]=1 }' infile.txt > outfile.txt

** Note: I wouldn't use this on a MASSIVE file, unless you're RAM-rich ;) **

Alternatives

There are 5 alternatives - vote for the best!

Terminal - Alternatives
perl -ane 'print unless $x{$F[0]}++' infile > outfile
2010-12-15 17:46:22
User: depesz
Functions: perl
3
F[0] filters using first word. $F[1] - 2nd, and so on.

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