help with hashes

[cantfindausername]

Me again...

I have a hash and I'm trying to access the keys using a specific value. Is it possible??

The simplest example I can give would be the following

#!/usr/bin/perl -w

%data =	(
	'Jan' => 31,
	'Feb' => 28,
	'Mar' => 31,
	'Apr' => 30);

$val = "31";

foreach $month (keys %data)
	{
	if ($val = $data{$val})
		{
		print "$month\n";
		}
	}

What I am trying to do is simple in my head, but maybe I'm not thinking "the perl way"? Or is there something I'm doing wrong?

Thanks in advance,
Anthony

 

[ishnid]

$val is numeric, so you shouldn't put quotes around it.

You're also using the wrong operator to test for equality. '=' is the assignment operator, so you're replacing the value in $val with $data{$val} each time. For numeric comparisons, you want '=='. Finally you should use $data{$month} rather than $data{$val}, as it's the month that's the hash key.

 

[cantfindausername]

Thanks for clearing those things up for me!

Hopefully this will give me the tools to go forward get over the hurdles I've got around this functionality.

Anthony

 

[MillerH]

[url=http://perldoc.perl.org/functions/use.html][black][b]use[/b][/black][/url] [green]Date::Calc[/green] [red]qw([/red][purple]Days_in_Month This_Year Month_to_Text[/purple][red])[/red][red];[/red]

[black][b]use[/b][/black] [green]strict[/green][red];[/red]

[olive][b]for[/b][/olive] [url=http://perldoc.perl.org/functions/my.html][black][b]my[/b][/black][/url] [blue]$month[/blue] [red]([/red][fuchsia]1..12[/fuchsia][red])[/red] [red]{[/red]
	[olive][b]if[/b][/olive] [red]([/red][maroon]Days_in_Month[/maroon][red]([/red]This_Year, [blue]$month[/blue][red])[/red] == [fuchsia]31[/fuchsia][red])[/red] [red]{[/red]
		[black][b]my[/b][/black] [blue]$abbrev[/blue] = [url=http://perldoc.perl.org/functions/substr.html][black][b]substr[/b][/black][/url] [maroon]Month_to_Text[/maroon][red]([/red][blue]$month[/blue][red])[/red], [fuchsia]0[/fuchsia], [fuchsia]3[/fuchsia][red];[/red]
		[url=http://perldoc.perl.org/functions/print.html][black][b]print[/b][/black][/url] [red]"[/red][purple][blue]$abbrev[/blue][purple][b]\n[/b][/purple][/purple][red]"[/red][red];[/red]
	[red]}[/red]
[red]}[/red]

[tt]------------------------------------------------------------
Pragmas (perl 5.8.8) used :
[ul]
[li]strict - Perl pragma to restrict unsafe constructs[/li]
[/ul]
Other Modules used :
[ul]
[li]Date::Calc[/li]
[/ul]
[/tt]

- Miller

 

[cantfindausername]

Thanks Miller. The example I was using above was the simplest version of what I was actually trying to do, but it was all sorted in the end. Good to know there are things like this though.

Ant

 

[brigmar]

.. and in the spirit of TIMTOWTDI and redundancy:

print join "\n", grep { $data{$_} == $val } keys %data;

...which combines the print, the if and the foreach into one statement.

(I'm still learning, and love to play around with map and grep at the moment. Forgive me.)