Cornelis Swanepoel wrote:
>> > Are you trying to find the intersection of two arrays? I believe this
>> > is covered in the FAQ,
>
>
> For simply finding the intersection of two arrays, is there something
> wrong
> with using nested greps?
>
> I'm a Perl beginner and after reading the first post I wrote this:
>
> my @arrA = qw( 1 3 5 6);
> my @arrB = qw( 2 3 6 4);
> my $tmp;
>
> my @matches = grep { $tmp = $_;
> grep $tmp == $_, @arrB;
> } @arrA;
>
> print join " ", @matches, "\n";
>
> It prints out
> 3 6
> for the above arrays.
>
> I've read the perlfaq snippet and it seems to be more elegant and flexible.
> I'd just like to know if there are any reasons, ie efficiency,
Yes, the FAQ answer is more efficient. Using Big O notation[1], the FAQ's
solution is O(n) and your's is O(n**2)
> I shouldn't
> use nested greps on simple lists like the above.
On simple lists it shouldn't make much of a difference.
> As I said, I am a Perl beginner and only want to deepen my understanding
> here so any comments would be greatly appreciated.
Limit the scope of the $tmp variable to the code block:
my @matches = grep { my $tmp = $_;
grep $tmp == $_, @arrB;
} @arrA;
[1] http://en.wikipedia.org/wiki/Big_O_notation
John
--
use Perl;
program
fulfillment
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