Adding arrays?

[Eric Schwartz]

On Wed, Jul 25, 2001 at 07:40:21PM -0600, Don Johnson wrote:
> Robert -
> 
> You solution will work fine.  The only trouble you might run into is if 
> you don't want to allow duplicate values in the resulting array.  If 
> @TempArray contains values already in @FinalArray, and you want to 
> disallow duplicates, you could use the keys of a hash to ensure no 
> duplicates:
> 
> %hash = ();
> foreach $key (@FinalArray) {
>     $hash{$key} = 1;    # we've seen this key
> }
> foreach $key (@TempArray) {
>     $hash{$key} = 1;    # we've seen this key
> }
> @FinalArray = keys %hash;

This is a great chance to use the handy perl language feature 'map'.  You
can do the exact same thing as this snippet above in two lines:

map { $hash{$_}++ } (@FinalArray, @TempArray);
@FinalArray = keys %hash;

'map' iterates over a list, and executes the associated code block once
for every item in the list, setting $_ to the item.  I've found that when
I feel the need to write a simple iterator, 90% of the time it's much
clearer and easier to use 'map'.

'grep' is similar to map, but it returns a list of all the items for
which the function returned true.  For instance, to extract all the items 
from @FinalArray that begin with the letter 'a':

@onlyAs = grep { /^a/ } @FinalArray;

That's my Fun Perl Hint Of The Day(tm).

-=Eric
-- 
Man usually avoids attributing cleverness to somebody else -- unless it
is an enemy.
    -- Albert Einstein