What is the best way to delete a value from an array in Perl?

Question

The array has lots of data and I need to delete two elements.

Below is the code snippet I am using,

my @array = (1,2,3,4,5,5,6,5,4,9);
my $element_o         


        

Answer 1

The best I found was a combination of "undef" and "grep":

foreach $index ( @list_of_indexes_to_be_skiped ) {
      undef($array[$index]);
}
@array = grep { defined($_) } @array;

That does the trick! Federico

Answer 2

Delete all occurrences of 'something' if array.

Based on SquareCog answer's:

my @arr = ('1','2','3','4','3','2', '3','4','3');
my @dix = grep { $arr[$_] eq '4' } 0..$#arr;
my $o = 0;
for (@dix) {
    splice(@arr, $_-$o, 1);
    $o++;
}
print join("\n", @arr);

Each time we remove index from @arr, the next correct index to delete will be $_-current_loop_step.

Answer 3

splice will remove array element(s) by index. Use grep, as in your example, to search and remove.

Answer 4

if you change

my @del_indexes = grep { $arr[$_] eq 'foo' } 0..$#arr;

to

my @del_indexes = reverse(grep { $arr[$_] eq 'foo' } 0..$#arr);

This avoids the array renumbering issue by removing elements from the back of the array first. Putting a splice() in a foreach loop cleans up @arr. Relatively simple and readable...

foreach $item (@del_indexes) {
   splice (@arr,$item,1);
}

Answer 5

Is this something you are going to be doing a lot? If so, you may want to consider a different data structure. Grep is going to search the entire array every time and for a large array could be quite costly. If speed is an issue then you may want to consider using a Hash instead.

In your example, the key would be the number and the value would be the count of elements of that number.

Answer 6

I use:

delete $array[$index];

Perldoc delete.