map many strings to one string in perl

Question

I want to do something like

$val = "value1"
my %test = ("value1" => "yes", "value2" => "yes", "value3" => "yes");
print  $test{$val};

So if either $val is equal to either value1, value2 or value3 then display "yes" otherwise display "no"

Not sure if I'm doing it the correct/efficient way. I'm new to perl

Really, you should test if the key exists, then test if the value is defined, then test if it's equal to "yes". Yay perl. — Matt K
– Matt K, Commented Sep 13, 2011 at 14:33
@mkb: assuming that the hash is static and is composed only out of constants, checking whether a value is undefined is unnecessary. — Blagovest Buyukliev
– Blagovest Buyukliev, Commented Sep 13, 2011 at 14:36
@mkb You only need to check for exists and defined if a valid value of the key may be 0 or ''. — TLP
– TLP, Commented Sep 13, 2011 at 14:54

Blagovest Buyukliev · Accepted Answer · 2011-09-13 14:45:13Z

3

You have to test whether a value with such a key exists in the hash:

print exists $tests{$val} ? $tests{$val} : "no";

In general, after checking for its existence, you have to check for its definedness via defined, but in your particular case this is not necessary since the %test hash seems to be constant and is composed only out of constants which do not include undef.

edited Sep 13, 2011 at 14:45

answered Sep 13, 2011 at 14:30

Blagovest Buyukliev

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1 Comment

TLP Over a year ago

You don't have to check if such a value exists. You only have to check if you want to use that particular value.

Alex Reynolds · Accepted Answer · 2011-09-13 14:30:59Z

2

if (defined $test{$val}) {
    print "$test{$val}\n";  # or you might use: print "yes\n"; depending on what you're doing
}
else {
    print "no\n";
}

answered Sep 13, 2011 at 14:30

Alex Reynolds

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Comments

Zaid · Accepted Answer · 2011-09-13 16:47:22Z

1

Is a hash the best possible data structure here when there are only two options? Here are three possible alternative subroutines that will equally satisfy the requirement:

sub test_ternary {
    $_[0] eq 'value1' ? 'yes' :
    $_[0] eq 'value2' ? 'yes' :
    $_[0] eq 'value3' ? 'yes' : 'no'  ;
}

sub test_regex { $_[0] =~ /value[123]/ ? 'yes' : 'no' }

use feature 'switch';
sub test_switch {
    given ( $_[0] ) {

        return 'yes' when /value[123]/;

        default { return 'no'; }
    }
}

answered Sep 13, 2011 at 16:47

Zaid

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2 Comments

Zaid Over a year ago

It is tempting to benchmark and micro-optimize the three alternatives ;)

mob Over a year ago

Don't forget smart match: print $value~~{"value1","value2","value3"]?"yes":"no"

TLP · Accepted Answer · 2011-09-13 14:59:35Z

0

Somewhat complicated answers here.

If the valid values in your hash can not be zero or empty string (or any other value which evaluates to "false" in perl), you can do:

say $test{$val} ? $test{$val} : "no";

This expression will be "false" if $test{$val} either does not exist, is undefined, is empty, or is zero.

answered Sep 13, 2011 at 14:59

TLP

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1 Comment

Eric Strom Over a year ago

say $test{$val} || 'no' if you are sure valid values in %test are always true

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