How do I shrink an array in Perl?

Question

How do I make an array shorter in Perl? I read some webpages indicating that I can assign:

$#ARRAY = 42;

I read that the use of $# is deprecated. I need a solution that will work for an array of arrays, too. This didn't work:

$#$ARRAY[$i] = 42;

Answer 1

I'm not aware of assigning $#ARRAY being deprecated; perldoc perldata from 5.10.0 certainly says nothing about it. It is the fastest way to truncate an array.

If you want something a little more readable, use splice:

splice @ARRAY, 43;

(Note 43 instead of 42 - $#ARRAY gets you the last index of the array, whereas splice taks the length of the array instead).

As for working on arrays of arrays, I assume you mean being able to truncate a nested array via a reference? In that case, you want:

$#{$ARRAY->[7]} = 42;

or

splice @{$ARRAY->[7]}, 43;

Answer 2

Your options are near limitless (I've outlined five approaches here) but your strategy will be dictated by exactly what your specific needs and goals are. (all examples will convert @array to have no more than $N elements)

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[EDIT]

As others have pointed out, the way suggested in the original question is actually not deprecated, and it provides the fastest, tersest, but not necessarily the most readable solution. It also has the side effect of expanding an array of fewer than $N elements with empty elements:

$#array = $N-1;

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Least code:

#best for trimming down large arrays into small arrays
@array = $array[0..($N-1)];

Most efficient for trimming a small number off of a large array:

#This is a little less expensive and clearer
splice(@array, $n, @#array);

Undesirable in almost all cases, unless you really love delete():

#this is the worst solution yet because it requires resizing after the delete
while($N-1 < $#array)
{
   delete(array[$i]);
}

Useful if you need the remainder of the list in reverse order:

#this is better than deleting because there is no resize
while($N-1 < $#array)
{
    pop @array;
    #or, "push $array2, pop @array;" for the reverse order remainder
}

Useful for saving time in long run:

#don't put more values into the array than you actually want