Looking up values in arrays?

[Benjamin Walkenhorst]

Hello everybody,

Is there a function to find out if a given value exists in an array?

What I think of is something like &has_element(\@array, $value), which
should return either a boolean value or the index containing the value
(undef if $value is not found).
I'm sure something like this exists. Or do I need to write this myself?


kind regards,

Benjamin

[Paul Johnson]

On Sun, Feb 15, 2004 at 08:26:08PM +0100, Benjamin Walkenhorst wrote:

> Is there a function to find out if a given value exists in an array?
>
> What I think of is something like &has_element(\@array, $value), which
> should return either a boolean value or the index containing the value
> (undef if $value is not found).
> I'm sure something like this exists. Or do I need to write this myself?

Something close exists. I think I'd probably code it as:

use List::Util "first";

sub has_element
{
my ($array, $value) = @_;
first { $_ eq $value } @$array
}

--
Paul Johnson - [email]paul@pjcj.net[/email]
[url]http://www.pjcj.net[/url]

[Benjamin Walkenhorst]

Hello,

On Sun, 15 Feb 2004 20:50:59 +0100
Paul Johnson <paul@pjcj.net> wrote:

> > I'm sure something like this exists. Or do I need to write this
> > myself?

>
> Something close exists. I think I'd probably code it as:

Thanks a lot! =)

Kind regards,

Benjamin

[Wiggins]

Benjamin Walkenhorst wrote:
 

This was just discussed in depth, check the archives for the last couple
of weeks. You may also want to read:

perldoc -f grep

http://danconia.org

[Jan]

Hi,

Benjamin Walkenhorst wrote:
 
>>
>> Something close exists. I think I'd probably code it as:[/ref]
>
>Thanks a lot! =)
>
>Kind regards,
>
>Benjamin
>[/ref]

And you could read the extensive thread named "Array containment" I startedrecently. I got several suggestions, including mapping to a hash and usinggrep.

- Jan
--
There are 10 kinds of people: those who understand binary, and those who don't

[R.]

Wiggins d'Anconia wrote:
 
>
> This was just discussed in depth,[/ref]

True, but this is the first time I've seen Paul's suggestion, or at least the
first time it has registered. I hope it will be offered more often, because it
is the most direct I've seen for similar needs.

Joseph

[Rob]

Paul Johnson wrote: 
>
> Something close exists. I think I'd probably code it as:
>
> use List::Util "first";
>
> sub has_element
> {
> my ($array, $value) = @_;
> first { $_ eq $value } @$array
> }[/ref]

Except that this will return the /value/ of the element
for which the block returns true, which isn't obvious from the
call. It's identical to

sub has_element {

my ($array, $value) = @_;

foreach (@$array) {
return $_ if $_ eq $value;
}

return;
}

which, to my mind, is preferable as it is clearer what's going on. It's
certainly no slower.

Rob

[David]

use List::Util "first";

sub has_element($$)
{
my( $aref, $value ) = @_;
first { $aref->[$_] eq $value } 0..$#$aref
}

?


-----Original Message-----
From: Rob Dixon [mailto:port995.com]
Sent: Monday, 16 February 2004 10:57 PM
To: org
Subject: Re: Looking up values in arrays?

Paul Johnson wrote: [/ref]
myself? 

Except that this will return the /value/ of the element for which the
block returns true, which isn't obvious from the call. It's identical to

sub has_element {

my ($array, $value) = @_;

foreach (@$array) {
return $_ if $_ eq $value;
}

return;
}

which, to my mind, is preferable as it is clearer what's going on. It's
certainly no slower.

Rob



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