Shell Programming and Scripting

I have searched the FAQ - by using sort, duplicates, etc.... but I didn't get any articles or results on it.

Currently, I am using:
sort -u file1 > file2 to remove duplicates. For a file size of 1giga byte approx. time taken to remove duplicates is 1hr 21 mins.

Is there any other faster way to remove duplicates? Our file sizes could get to 10 to 12 giga bytes size.

Aprpeciate any pointers.
Thanks,
Radhika.

Just a thought.

Why not use the divide and conquer approach ?

Vino

That's about 200KB/s. Pretty crap.
I presume you're thrashing swap?

One thing to check is if you don't need multibyte sorting,
then prepend the sort command with LANG=C

Sounds like you need a database (indexes) to be honest.

If the output is a small % of the input, then
explicitly partitioning the input would be beneficial.
I.E.: while sort -u chunk | sort -u

Try out this one...

sed '$!N; /^\(.*\)\n\1$/!P; D'

# The first line of duplicate ones is only kept and rest are deleted.

I have tested this with around 1GB file.

it took about 13 min to sort that file. Much Much Faster than sort command.

Havn't tried your sed. But doesnt it assume that all the entries are already sorted and then it removes the duplicates.

and/or

If the file is unsorted, then duplicate entries based on first line are removed. since sed makes just one-pass through the file.

Or did I get it wrong ?

vino

Hi Vino,

This command will keep the first entry as it is and delete the other entries,

irrespective of whether the file is sorted or not.

No prior assumptions while executing this command.

Hi Amit,


>>
sed '$!N; /^\(.*\)\n\1$/!P; D'

Could you explain the command - bit by bit if you don't mind.

Thanks!