Re: What defines the choice of a Hash or an Array?

[thinker]

Hi ghenry,

When I am thinking of my code, there are two words which I look out for which suggest I might want ot use a hash. Those words are "of" and "contains" (or its more perlish alternative, exists).

An example of "of" might be

my %capitals = (France => "Paris",
                Scotland => "Edinburgh",
                );
# find the capital "of" Scotland
print $capitals{"Scotland"}, "\n";

The fast access speed of hashes makes it a good candidate to find the intersection of two lists. For (a rather contrived) example

# we have a pre-prepared list of prime numbers
my @primeslist  =  qw(2 3 5 7 11 13 17 19 23 29);

# populate a hash with the primes as keys
# this allows for fast retrieval
my %primes;
@primes{@primeslist} = ();

# now we can loop through our new list ( 1 .. 30)
# using the exists() function to (quickly) check if a key exists
print "$_ is prime\n" for grep exists $primes{$_}, 1 .. 30;

Hope this helps

thinker

[ghenry]

Thanks thinker.