comparing array elements

[Anonymous Monk]

Dear monks, I wondered if someone could show me a way of comparing each position in two arrays to see if they contain the same value. Is a hash the best way to do this?

Many thanks!

e.g.  $array[0] with $array2[0] etc...

[Roger]

Why complicate the issue with a hash? You can do that (efficiently) with the simplest for loop. :)



die "arrays different sizes" if $#array1 != $#array2;

my $match = 1;                # assume arrays match
foreach (0..$#array1) {       # unless otherwise
    $match = 0, last if $array1[$_] ne $array2[$_];
}

if ($match) {
   # arrays match
   ....
}

[BrowserUk]

If you only need to know if the two arrays are identical, you can cheat a little by using join and eq.

@a = qw[1 2 3 4 5]; 
@b = qw[1 2 3 4 5]; 
@c = qw[1 2 3 4 6];

print "a is equivalent to b" if join("\0", @a) eq join("\0", @b);

a is equivalent to b

print "a is equivalent to c" if join("\0", @a) eq join("\0", @c);

This requires that you data doesn't contain nulls, and it will consume a large amount ram (breifly) if the arrays are large.

However, if you need to know where and/or what the differences are, then there is no avoiding a loop.

---

Examine what is said, not who speaks.
"Efficiency is intelligent laziness." -David Dunham
"Think for yourself!" - Abigail
Hooray!
Wanted!

[rir]

Update: I missed the doesn't contain nulls caveat in the previous post. I have no point.

[Abigail-II]

That's a FAQ. perldoc -q intersection.

Abigail

[Anonymous Monk]

Hi Abigail-II, the problem is that intersection works on the whole list, I need to work on individual elements in the same position.

[Abigail-II]

At first, I thought that too. But then you were considering to use a hash.

What have you tried so far?

Abigail