Comparing 2 large arrays

ansrewdps · 08-05-2011, 08:01 PM

Can anone help me in writing some code that compares 2 large arrays. I know we can do that using 2 loops incrementing each element in the outer loop and comparing that to the second array.
But if that's an large array that would be computationally intensive...
So, I'm trying to develop a code that compares two arrays and print equal if two arrays(large) are equal(order of the elements doesn't matter).

any code in C/Perl??

Thanks
Andrew

anomie · 08-05-2011, 08:09 PM

As of Perl 5.10, you can simply do:

Code:

if(@foo ~~ @bar)

That's the smart match operator. Details on what it's testing in perlsyn(1).

---

edit: On second thought, given that you said "order of the elements doesn't matter", you may need to sort first and/or try a different approach. (You'll see what I mean when you read perlsyn(1).)

devnull10 · 08-05-2011, 08:23 PM

In an unordered array, the computation is always going to be of order n*m for arrays of size n & m.

ansrewdps · 08-05-2011, 08:34 PM

Thanks for the quick reply....I tried writing a code but ended up getting errors...can you help me with the code

#! /usr/bin/perl
use warnings

#initializing queries
@qw=qw ! perl java python Ms.Net !;
@pw= qw ! Ms.Net perl java python !;

if(@qw ~~ @pw)
{
print 'arrays equal';
}
else
{
print 'arrays not equal';
}

#./demo.pl
Unknown warnings category 'perl' at ./demo.pl line 5
BEGIN failed--compilation aborted at ./demo.pl line 5.

ansrewdps · 08-05-2011, 08:44 PM

I got that working but it returns array not equal cause the order of the elements are different...As said,elements are tested not the order which they are in the array...

any idea on how to make it work? and can you give me walkthrough on how exactly this work?

will this work as the same way as implementing in 2 for loops incrementing inner loop first and then outer loop??

Thanks

jcmlq · 08-05-2011, 09:20 PM

Code:

#! /usr/bin/perl
use warnings;

#initializing queries
@qw=qw ! perl java python Ms.Net !;
@pw= qw ! Ms.Net perl java python !;

if(sort(@qw) ~~ sort(@pw))
{
  print 'arrays equal';
}
else
{
  print 'arrays not equal';
}

Since order does not matter, you need to sort the lists first. This is desirable in any case, because you would have to walk the entire compared list for each element otherwise.

Code:

# don't do this, it's wasteful

foreach $i (@pw)
{
  foreach $j (@qw)
  {
    if ($i == $j)
    {
      ...