Re: deleting duplicates in array using references
- From: Paul Lalli <mritty@xxxxxxxxx>
- Date: Mon, 30 Jul 2007 18:42:29 -0700
On Jul 30, 5:18 pm, billb <billbea...@xxxxxxx> wrote:
On 30 Jul, 19:46, Paul Lalli <mri...@xxxxxxxxx> wrote:
On Jul 30, 2:37 pm, billb <billbea...@xxxxxxx> wrote:
i have a multidimensional array, but i want to delete duplicate
entries based on the first element of each 'row'.
my @array = ( [UK9004411, A140, B, 0.040] , [UK0030239, H7140, H,
0.030] , [UK0030239, S1393, M1, 0.030] , [UK0012821, H4030, H,
0.010] , [UK0012821, H4060, H, 0.010] );
and I want to end up with
( [UK9004411, A140, B, 0.040] , [UK0030239, H7140, H, 0.030] ,
[UK0012821, H4030, H, 0.010] )
my %seen;
my @nodups = grep { !$seen{$_->[0]}++ } @array;
ah, very simple and very fast as well! I'll have to understand how
this is working. It uses a hash I see.
It helps if you expand it out to remove all the "shortcuts"
my %seen;
my @nodups;
foreach my $elem (@array) {
if (! $seen{$elem->[0]}) {
push @nodups, $elem;
}
$seen{$elem->[0]}++;
}
So we're looping through the 2d array, and we check to see if the
first element of the current array reference has been "seen" yet. If
not, we add this array reference to our list of no duplicates. Then
we increment the number of times we've "seen" this element, so that if
the same element is seen again, we won't add it next time.
The shortcuts:
* a foreach-if-push combination is equivalent to grep(). grep selects
only those elements from a list for which the if condition holds.
* in the grep, $_ is used to represent the current element of the
array (rather than $elem as in the above expansion)
* The ++ operator is applied to the same expression as when we're
checking the current value of $seen{$_->[0]}, because a post-fix ++
increments the value *after* returning that value. That is:
$x = $foo++;
is equivalent to:
$x = $foo;
$foo++;
In contrast,
$x = ++$foo;
is equivalent to
$foo++;
$x = $foo;
Many thanks.
You're welcome
Paul Lalli
.
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- From: billb
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- From: Paul Lalli
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