Array refs problem ...

Tharg has asked for the wisdom of the Perl Monks concerning the following question:

Hi Monks - I have been trying to do this (tested and working as intended, gives "-->a,4,6<--" out) :

use strict;

my(@Array1);

my(@Array2);

@Array1     = (0,1,'a',3,4,5,6);

@Array2     = (2,4,6);

@Array1    = @Array1[ ( @Array2 ) ];

printf STDOUT ("-->%s<--\n", join( ",",  @Array1 ) );
[download]

But with array references. My line looks like this :

@{ $Row->{ Cells } }    = @{ $Row->{ Cells }[ ( @$FieldOrder ) ] };
[download]

But I'm getting 'Not an ARRAY reference' errors. Thanks in advance, and apologies for what is probably a basic question.

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Re: Array refs problem ... by ikegami (Patriarch) on Jun 24, 2009 at 16:20 UTC
Find out which array dereference isn't getting the array reference it expects. `$Row->{ Cells }`? `$FieldOrder`? `$Row->{ Cells }[ ( @$FieldOrder ) ]`? Update: Your use of `0+@$FieldOrder` is very suspicious. Update: You have an array slice in the top code (note the "`@`" in `@Array1[ LIST ]`), but you have an array lookup in the bottom code (note the "`$`" in `$Row->{ Cells }[ SCALAR ]`) The equivalent of `@Array1[ LIST ] ^ \|` [download] is `@{ $array_ref }[ LIST ] ^ \|` [download] You want `@{ $Row->{ Cells } } = @{ $Row->{ Cells } }[ @$FieldOrder ];` [download] See Dereferencing Syntax and References Quick Reference.	[reply] [d/l] [select]
Re^2: Array refs problem ... by Tharg (Scribe) on Jun 24, 2009 at 16:35 UTC
Yeah I think the problem is with the way I'm dong that somehow. Adding : `printf STDOUT ("1-->%s<--\n", $Row->{ Cells } ); printf STDOUT ("2-->%s<--\n", $FieldOrder ); printf STDOUT ("3-->%s<--\n", $Row->{ Cells }[ ( @$FieldOrder ) ] ) ;` [download] Gave me `1-->ARRAY(0x2af07dc)<-- 2-->ARRAY(0x2ab07dc)<-- 3-->HASH(0x2b50058)<--` [download] I don't know what I would have expected for the last one (I think that's like saying `$Array[1..4]`, which surely should be written `@Array[1..4]`, but what do I know ...) Update Thanks, but tried that first, didn't work, same error. Update2 Oh wait, I missed that you removed the ( ) around @$FieldOrder also, I seem to be making progress now. Many thanks!	[reply] [d/l] [select]
Re^3: Array refs problem ... by ikegami (Patriarch) on Jun 24, 2009 at 17:44 UTC
Oh wait, I missed that you removed the ( ) around @$FieldOrder also, I seem to be making progress now. Many thanks! Only because they were distracting. They have absolutely no effect here. Just like you wouldn't use `$z=($x)+($y)` instead of `$z=$x+$y`, there's no reason to use `@a[(@$b)]` instead of `@a[@$b]`.	[reply] [d/l] [select]
Re: Array refs problem ... by NetWallah (Canon) on Jun 24, 2009 at 19:58 UTC
I think what you are trying to do is: `$Row->{ Cells } =[ @{ $Row->{ Cells } }[ @$FieldOrder ] ];` [download] The @{ $Row->{ Cells } } is the array , which you slice using [ @$FieldOrder ]; Then generate an anonymous array ref (The outermost [ ] ) The anon array ref is assigned to the scalar $Row->{ Cells } , Potentia vobiscum ! (Si hoc legere scis nimium eruditionis habes)	[reply] [d/l]
Re: Array refs problem ... by mscharrer (Hermit) on Jun 24, 2009 at 16:47 UTC
I agree with ikegami's post above. You should try to avoid to surround the arrays with `( )`'s. This is (IMHO) never necessary and just adds another pair to be tracked by the programmer/maintainer/whoever read the source code. Also the double line spacing used here makes the code a little less readable.	[reply] [d/l]