Re: Use Hash? Array? Still confused after all these years.

Everyone posted their own views of how and when to use hashes. Problem is that it's really hard to explain in plain words.

I believe it's hard because it either clicks in your head or not. Well at least it's case with me - once I was introduced to hashes I simply got them as granted.

As someone pointed out - you use hashes for storing any data that has names. Such as database tables and forms. Sometimes it's also good to use hash as a parameter for some function/method (often referred as PARAMHASH). In cases when you have more than few parameters.

Anyway if I understood you - I would use following:
- hash for storing the form data > you get it from CGI that way
- hash for storing file names. As keys you have state options, and as matching values you have file names.

So it ends up with something like:

my $request = CGI->new();

# Is it a hashref or plain hash ?!?
my $values = $request->Vars();

# Or maybe coming from a config file
my %files = { state1 => 'filename1.csv',
              state2 => 'filename2.csv',
              default => 'default_filename.csv',
            }

my $file_name = $files{default};

if(defined $files{$values{state}}) {
   $file_name = $files{$values{state};
}

# Or something shorter like :
# my $file_name = $files{$values{state}} || $files{default}; 

#open....
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Comment on Re: Use Hash? Array? Still confused after all these years. Download Code

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Re^2: Use Hash? Array? Still confused after all these years. by Anonymous Monk on Jul 23, 2005 at 02:16 UTC
You've gone 5 years without learning hashes? Pick up a copy of Learning Perl, and work through it all the way. It will serve you well. Conceptually, you'll want to do something like this: # first, tell perl you want a local version of a hash called filename my %filename; # put in the data for your states %filename ( state1 => "FileA.csv", state2 => "FileB.csv", state3 => "FileC.csv"); # The above statement is the same as writing the three commented lines + below. It's prefered because it's simpler, and requires less typing, + so it has lower odds for a mistake. Perhaps the lines below are clea +rer to a beginner, though... they do the same thing as the line above +. #$filename{"state1"}="FileA.csv"; #$filename{"state2"}="FileB.csv"; #$filename{"state3"}="FileC.csv"; # get your state variable somehow... say from a function called get_st +ate() $state = get_state(); $file = $filename{ $state }; # The above statement a just looks for a matching value for $state in +the hash. If it can't find one, uses the undefined value instead. It +assigns whatever value it came up with to $file. It's like writing th +e following big if statement, but again, with less repetition... # if ( $state eq "state1" ) { # $file = "FileA.csv"; # } elsif ( $state eq "state2" ) { # $file = "FileB.csv"; # } elsif ( $state eq "state3" ) { # $file = "FileC.csv"; # } else { # $file = undef(); # } [download]	[reply] [d/l]
Re^3: Use Hash? Array? Still confused after all these years. by hmbscully (Scribe) on Jul 26, 2005 at 20:55 UTC
I appreciate your response, but in my question I did note that I do have Learning Perl, aka the llama, I've had a copy forever. I know I need to work it through again.	[reply]


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