Re: Empty Array

[James Edward Gray II]

On Jan 2, 2004, at 10:18 AM, Jeff Westman wrote:

What is the proper way to test if an array is empty ?
Probably the easiest is:

if (@array) {
# not empty
}
else {
# empty
}
# or...

unless (@array) {
# empty
}
This works because an array in scalar context returns the number of 
elements it contains.  If it contains 0, that will equate to false.  
Anything else will be true.

James

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Empty Array

[Jeff Westman]

What is the proper way to test if an array is empty ?


TIA

-JW

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Re: How Do I initialize an empty array

[Tore Aursand]

On Tue, 28 Oct 2003 11:53:44 -0700, Wiggins d Anconia wrote:
> or if you know the length of the array ahead of time:
> 
> my @rows = ('','','');

I prefer the following instead:

  my @rows = ('') x 3;

Easier to read...?


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Re: How Do I initialize an empty array

[Rob Dixon]

<[EMAIL PROTECTED]> wrote:
>
> How Do I initialize an empty array so thtat I don't get an unitiialized
> error?
>
> ...
> my @rows;
>
> I thought I could do something like @rows = new (); but it's not working.

You don't.

  my @rows;

declares an array, which is initially empty. If you put
something into it and want it back like it was, then

  @rows = ()

will empty it again.

If you're getting 'Use of uninitialized value' then it's
because you're using an element of the array that hasn't
been assigned (or has been asigned with 'undef').

Rob



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Re: How Do I initialize an empty array

[perl]

thanks. it works.
@rows=();

--
>
>
>> How Do I initialize an empty array so thtat I don't get an unitiialized
>> error?
>>
>> ...
>> my @rows;
>>
>> I thought I could do something like @rows = new (); but it's not
>> working.
>>
>
> Drop the 'new':
>
> my @rows = ();
>
> http://danconia.org
>



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Re: How Do I initialize an empty array

[Wiggins d Anconia]

> 
> 
> > How Do I initialize an empty array so thtat I don't get an unitiialized
> > error?
> > 
> > ...
> > my @rows;
> > 
> > I thought I could do something like @rows = new (); but it's not
working.
> > 
> 
> Drop the 'new':
> 
> my @rows = ();
> 

Are you sure you are getting the warning on the array or on the elements
of the array you are using?  In which case you can check for
definedness, before using the value, 

perldoc -f defined

or if you know the length of the array ahead of time:

my @rows = ('','','');

For a three element array

http://danconia.org

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Re: How Do I initialize an empty array

[Wiggins d Anconia]

> How Do I initialize an empty array so thtat I don't get an unitiialized
> error?
> 
> ...
> my @rows;
> 
> I thought I could do something like @rows = new (); but it's not working.
> 

Drop the 'new':

my @rows = ();

http://danconia.org

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How Do I initialize an empty array

[perl]

How Do I initialize an empty array so thtat I don't get an unitiialized
error?

...
my @rows;

I thought I could do something like @rows = new (); but it's not working.

thanks


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Re: Check for empty array

[Dharmender Rai]

Yes you are right !!

Thanx

Dharmender Rai

 --- "John W. Krahn" <[EMAIL PROTECTED]> wrote: >
Dharmender rai wrote:
> > 
> > You can use defined() function by checking for the
> > first element.
> 
> No, checking the first element of an array will tell
> you whether or not
> the first element of the array is defined, it will
> not tell you if the
> array is empty.
> 
> 
> John
> -- 
> use Perl;
> program
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Re: Check for empty array

[John W. Krahn]

Dharmender rai wrote:
> 
> You can use defined() function by checking for the
> first element.

No, checking the first element of an array will tell you whether or not
the first element of the array is defined, it will not tell you if the
array is empty.


John
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Re: Check for empty array

[Michael Fowler]

I just noticed this thread, so forgive me if someone has already mentioned
this, or if I'm missing the original point.  I just saw some bad examples of
how to accomplish what the subject asks, and felt I should chime in.

The idiomatic method for checking if an array has elements is simply:

if (@array) { ... }

If you've stored an array reference, as in $ref = \@array, then dereference:

if (@$ref) { ... }

See perldoc perldata for help on dealing with data types, perldoc perlref
and perldoc perldsc for help on dealing with references.


Checking an individual element to see if an array is empty will not work. 
One of the examples was:

if (!defined $ref->[0]) { ... }

Given:

@array = (undef, "foo", "bar");
$ref = \@array;

That test will return a false positive; defined($ref->[0]) will be false,
yet there are elements in @array, and by extension, @$ref.


Another of the examples was:

if (!$array[0]) { ... }

Given:

@array = (0, "foo", "bar");

That test will also return a false positive; $array[0] is false, yet there
are elements in @array.


Michael
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Re: Check for empty array

[Dharmender Rai]

You can use defined() function by checking for the
first element.
#!/usr/bin perl
use strict;
use warnings;

my @arr=(); ## empty
my $ref=\@arr; ##

if(!defined ($ref->[0]) { 
# do your work here
}

if (!define ($arr->[0]) {
# do your work
}

 --- dan <[EMAIL PROTECTED]> wrote: > or
> 
> if (!$array[0]) {
>  # it's empty
> }
> 
> your choice :)
> 
> dan
> 
> "Nikola Janceski" <[EMAIL PROTECTED]>
> wrote in message
>
[EMAIL PROTECTED]">news:[EMAIL PROTECTED]...
> > if(not @array){
> > # it's empty
> > }
> >
> > > -Original Message-
> > > From: Bryan Harris [mailto:[EMAIL PROTECTED]]
> > > Sent: Friday, October 04, 2002 11:58 AM
> > > To: Beginners Perl
> > > Subject: Check for empty array
> > >
> > >
> > >
> > >
> > > What's the easiest way to check whether an array
> is empty?
> > >
> > > I'm really feeling like a beginner today...
> > >
> > > - Bryan
> > >
> > >
> > > --
> > > To unsubscribe, e-mail:
> [EMAIL PROTECTED]
> > > For additional commands, e-mail:
> [EMAIL PROTECTED]
> > >
> >
> >
>
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> and opinions of Summit
> > Systems Inc.
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Re: Check for empty array

[James Edward Gray II]

On Friday, October 4, 2002, at 11:21  AM, dan wrote:

> or
>
> if (!$array[0]) {

This tests for a "true" value in the first element of an array, not if  
it's empty.  This test will succeed for the list (undef, 1, 2, "More  
Data"), which is definitely not empty.

>  # it's empty
> }
>
> your choice :)
>
> dan
>
> "Nikola Janceski" <[EMAIL PROTECTED]> wrote in message
> [EMAIL PROTECTED]">news:[EMAIL PROTECTED] 
> ...
>> if(not @array){
>> # it's empty
>> }
>>
>>> -Original Message-
>>> From: Bryan Harris [mailto:[EMAIL PROTECTED]]
>>> Sent: Friday, October 04, 2002 11:58 AM
>>> To: Beginners Perl
>>> Subject: Check for empty array
>>>
>>>
>>>
>>>
>>> What's the easiest way to check whether an array is empty?
>>>
>>> I'm really feeling like a beginner today...
>>>
>>> - Bryan
>>>
>>>
>>> --
>>> To unsubscribe, e-mail: [EMAIL PROTECTED]
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>>
>> -- 
>> 
> --
>> 
>> The views and opinions expressed in this email message are the  
>> sender's
>> own, and do not necessarily represent the views and opinions of Summit
>> Systems Inc.
>>
>
>
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Re: Check for empty array

[Jeremy Vinding]

On Fri, 2002-10-04 at 10:21, [EMAIL PROTECTED] wrote:
> or
> 
> if (!$array[0]) {
>  # it's empty
> }
> 
> your choice :)
> 
> dan

not quite... try that on this array:
@array = qw(0 1 2 3 4 5 6);

jjv


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Re: Check for empty array

[dan]

or

if (!$array[0]) {
 # it's empty
}

your choice :)

dan

"Nikola Janceski" <[EMAIL PROTECTED]> wrote in message
[EMAIL PROTECTED]">news:[EMAIL PROTECTED]...
> if(not @array){
> # it's empty
> }
>
> > -Original Message-
> > From: Bryan Harris [mailto:[EMAIL PROTECTED]]
> > Sent: Friday, October 04, 2002 11:58 AM
> > To: Beginners Perl
> > Subject: Check for empty array
> >
> >
> >
> >
> > What's the easiest way to check whether an array is empty?
> >
> > I'm really feeling like a beginner today...
> >
> > - Bryan
> >
> >
> > --
> > To unsubscribe, e-mail: [EMAIL PROTECTED]
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> >
>
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> The views and opinions expressed in this email message are the sender's
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Re: Check for empty array

[John W. Krahn]

Bryan Harris wrote:
> 
> What's the easiest way to check whether an array is empty?

An array in a scalar context returns the number of elements in the
array.

if ( @array == 0 ) { # explicit test for zero elements

unless ( @array ) { # implicit test for zero elements


John
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Re: Check for empty array

[James Edward Gray II]

HANDLE_EMPTY() unless @array;

James Gray

On Friday, October 4, 2002, at 10:57  AM, Bryan Harris wrote:

>
>
> What's the easiest way to check whether an array is empty?
>
> I'm really feeling like a beginner today...
>
> - Bryan
>
>
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RE: Check for empty array

[Nikola Janceski]

if(not @array){
# it's empty
}

> -Original Message-
> From: Bryan Harris [mailto:[EMAIL PROTECTED]]
> Sent: Friday, October 04, 2002 11:58 AM
> To: Beginners Perl
> Subject: Check for empty array
> 
> 
> 
> 
> What's the easiest way to check whether an array is empty?
> 
> I'm really feeling like a beginner today...
> 
> - Bryan
> 
> 
> -- 
> To unsubscribe, e-mail: [EMAIL PROTECTED]
> For additional commands, e-mail: [EMAIL PROTECTED]
> 



The views and opinions expressed in this email message are the sender's
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Systems Inc.


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Check for empty array

[Bryan Harris]

What's the easiest way to check whether an array is empty?

I'm really feeling like a beginner today...

- Bryan


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