PERL: comaprying an array with the permuation of another arr

Posts: 3 · Posted: Tue Jul 25, 2006 9:03 pm

Hi there,

Does anyone know how to compare an array in perl with another array ? I mean I want to compare the array with the permutation of another array. For example,

@a = {2,1,3};
@b={1,3,2}; // any one of the permuation of this array should match with @a.
@c = {5,4,2};

When I compare @a with @b, it should return true where as when I compare @a with @c, it should return false. I really need to know this.

Thank you in advance,
priya

Posts: 22 · Posted: Thu Jul 27, 2006 11:53 am

The simple way would be to first sort the array before comparing.

But, my question is, how are you comparing? Are you doing a "if (@a == @b)"? That wouldn't work.

I found this thread on PerlMonks that would give you some ideas on many ways to handle an array comparison.
http://perlmonks.org/?node_id=335021[/img]

Posts: 17 · Posted: Fri Mar 30, 2007 9:25 pm

Code:

sub compArray
# compare two arrays
# use: compArray(\@one,\@two)
# returns 1 for same 0 for different
# stupid obfuscated version
# optimised for speed - no local vars
{
if (@{$_[0]} != @{$_[1]}) { return 0; } # test lengths
foreach (0 .. $#{$_[0]}) # go element by element
{
if ($_[0][$_] ne $_[1][$_]) {return 0;}
}
return 1; # If I got here we are good
}

Example how to use

Code:

my @a = (1,2,3);
my @b = (1,2,3);
if ( compArray(\@a,\@b )){ print "True\n";}else{print "False\n";}

NOTE THIS WILL NOT WORK WITH RECURSIVE STUFF

Slight mod will work

Code:

sub compArrayRec
{
if (@{$_[0]} != @{$_[1]}) { return 0; } # test lengths
foreach (0 .. $#{$_[0]}) # go element by element
{
if (UNIVERSAL::isa($_[0][$_],"ARRAY") and
UNIVERSAL::isa($_[1][$_],"ARRAY") )
)
{
if (!compArrayRec($_[0][$_],$_[1][$_])){return 0;}
}
else
{
if ($_[0][$_] ne $_[1][$_]) {return 0;}
}
}
return 1;
}

and usage

Code:

my @a = (1,2,3,[1,2,3]);
my @b = (1,2,3,[1,2,3]);
if ( compArrayRec(\@a,\@b )){ print "True\n";}else{print "False\n";}

I leave it up to the reader to figure it out for Hashes too

Posts: 178 · Posted: Tue Apr 03, 2007 9:52 am

the above is why Ruby pwns Perl any day of the week. this should work:

Code:

class Array
def lazy_eql?(a)
   raise ArgumentError unless a.is_a? Array # verify we got an array

   # verify number of elements, then merge & check again
   return (a.length == self.length && (a | self).length == self.length)
end
end

Let's see:

Code:

t = ["a", "b", "c"]
t1 = ["a", "b", "b"]
t2 = ["c", "b", "a"]

t.lazy_eql? t1
=> false
t.lazy_eql? t2
=> true

Now which code do you want to be responsible for maintaining?