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Re: find position of element of array
by friedo (Prior) on Nov 07, 2005 at 07:00 UTC
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To find the index of an element within an array, you can grep.
my ($index) = grep { $array[$_] eq 'c' } 0..$#array;
Then just subtract one from $index. (Watch out of $index happens to be zero though.)
Update: Forgot list context for $index.
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Wow, and all this time I've been doing variations of
for (my $i = 0; $i < @foo; ++$i) {
if ($foo[$i] eq $match_element) {
return $i;
}
}
just another cpan module author
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Re: find position of element of array
by Anonymous Monk on Nov 07, 2005 at 07:33 UTC
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Can't believe this hasn't been pointed out yet, but @array = {"a", "b", "c", "d"} leaves @array with one element, that element being a hashref. You want parentheses instead of braces.
Instead of the grep solution offered above, you can use List::Util's first.
#!/usr/bin/perl -l
use List::Util "first";
my @array = qw(a b c d);
my $index = first { $array[$_] eq "c" } 0..$#array;
die "c was not found in \@array" if ! defined $index;
print $array[$index-1];
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Hi Guys,
I tried this code. At first I thought it was working fine. But now I see that there is a small problem with this code.
The problem is : the index is circular (semi circular I guess). That means, if my array is @a = {"a", "b", "c", "d", "e"} and I want to find the element before "a", it should be undefined. But when I print the element before "a" using the above method and (defined $array$index -2), I get "e".
Also, it is strange that when I check like: if (defined $array$index +2), that element is correctly not defined.
If you understand this problem, please help me out.
Thanks
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Just check for the returned index being 0 and handle that special case appropriately. Negative indexes count backwards, so in your above array $a[-1] will correctly return "e". $a[5] will be undef, because the array only contains values for @a[0..4]. Take a look at perldoc perldata for more details on arrays.
BTW, you should add <code></code> tags around the code in your posts, otherwise it comes out mangled.
Debugging is twice as hard as writing the code in the first place. Therefore, if you write the code as cleverly as possible, you are, by definition, not smart enough to debug it. -- Brian W. Kernighan
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Re: find position of element of array
by tirwhan (Abbot) on Nov 07, 2005 at 08:42 UTC
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use List::MoreUtils qw(firstidx);
my @array = ("a","b","c","d");
my $index = firstidx { $_ eq "c" } @array;
my $wanted = $array[$index - 1];
Debugging is twice as hard as writing the code in the first place. Therefore, if you write the code as cleverly as possible, you are, by definition, not smart enough to debug it. -- Brian W. Kernighan
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Note that this code will assign "d" to $wanted if searching with "a".
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Re: find position of element of array
by stonecolddevin (Parson) on Nov 07, 2005 at 07:00 UTC
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if it's going to be consistently like this, you can do:
my $element = $array[$element_to_retrieve-1];
Where $element_to_retrieve is the variable you're passing to obtain the element you want in the array...
(untested)
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