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perl, check if data exists in array

Posted on 2010-11-17
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Last Modified: 2012-06-21
# DEFINE AN ARRAY
@coins = ("Quarter","Dime","Nickel");
my $money = "Dime";

How do I check if Dime is one of the value in the array?  Would be nice if i don't have to loop through it.
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Question by:rgbcof
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3 Comments
 
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Accepted Solution

by:
whosbetterthanme earned 125 total points
ID: 34159681
Simple:

@coins = ("Quarter","Dime","Nickel");
my $money = "Dimes";

if (grep(/$money/,@coins)) {
print "Yep, it's there\n";
}
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Author Closing Comment

by:rgbcof
ID: 34159727
That works.  
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Expert Comment

by:ozo
ID: 34161953
perldoc -q "How can I tell whether a certain element is contained in a list or array"
Found in pods/perlfaq4.pod
       How can I tell whether a certain element is contained in a list or
       array?

       (portions of this answer contributed by Anno Siegel)

       Hearing the word "in" is an indication that you probably should have
       used a hash, not a list or array, to store your data.  Hashes are
       designed to answer this question quickly and efficiently.  Arrays
       aren't.

       That being said, there are several ways to approach this.  If you are
       going to make this query many times over arbitrary string values, the
       fastest way is probably to invert the original array and maintain a
       going to make this query many times over arbitrary string values, the
       fastest way is probably to invert the original array and maintain a
       hash whose keys are the first array's values.

               @blues = qw/azure cerulean teal turquoise lapis-lazuli/;
               %is_blue = ();
               for (@blues) { $is_blue{$_} = 1 }

       Now you can check whether $is_blue{$some_color}.  It might have been a
       good idea to keep the blues all in a hash in the first place.

       If the values are all small integers, you could use a simple indexed
       array.  This kind of an array will take up less space:

               @primes = (2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31);
               @is_tiny_prime = ();
               for (@primes) { $is_tiny_prime[$_] = 1 }
               # or simply  @istiny_prime[@primes] = (1) x @primes;

       Now you check whether $is_tiny_prime[$some_number].

       If the values in question are integers instead of strings, you can save
       quite a lot of space by using bit strings instead:

               @articles = ( 1..10, 150..2000, 2017 );
               undef $read;
               for (@articles) { vec($read,$_,1) = 1 }

       Now check whether "vec($read,$n,1)" is true for some $n.

       These methods guarantee fast individual tests but require a re-
       organization of the original list or array.  They only pay off if you
       have to test multiple values against the same array.

       If you are testing only once, the standard module "List::Util" exports
       the function "first" for this purpose.  It works by stopping once it
       finds the element. It's written in C for speed, and its Perl equivalent
       looks like this subroutine:

               sub first (&@) {
                       my $code = shift;
                       foreach (@_) {
                               return $_ if &{$code}();
                       }
                       undef;
               }

       If speed is of little concern, the common idiom uses grep in scalar
       context (which returns the number of items that passed its condition)
       to traverse the entire list. This does have the benefit of telling you
       how many matches it found, though.

               my $is_there = grep $_ eq $whatever, @array;

       If you want to actually extract the matching elements, simply use grep
       in list context.

               my @matches = grep $_ eq $whatever, @array
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