How do I initialize an array to 0?
I have tried this.
my @arr = ();
But it always throws me a warning, "Use of uninitialized value". I do not know the size of the array beforehand. I fill it dynamically. I thought the above piece of code was supposed to initialize it to 0.
How do I do this?
If I understand you, perhaps you don't need an array of zeroes; rather, you need a hash. The hash keys will be the values in the other array and the hash values will be the number of times the value exists in the other array:
use strict;
use warnings;
my @other_array = (0,0,0,1,2,2,3,3,3,4);
my %tallies;
$tallies{$_} ++ for @other_array;
print "$_ => $tallies{$_}\n" for sort {$a <=> $b} keys %tallies;
Output:
0 => 3
1 => 1
2 => 2
3 => 3
4 => 1
To answer your specific question more directly, to create an array populated with a bunch of zeroes, you can use the technique in these two examples:
my @zeroes = (0) x 5; # (0,0,0,0,0)
my @zeroes = (0) x @other_array; # A zero for each item in @other_array.
# This works because in scalar context
# an array evaluates to its size.
if (def $value) { push(@array,$value) } else { push(@array,"") }.What do you mean by "initialize an array to zero"? Arrays don't contain "zero" -- they can contain "zero elements", which is the same as "an empty list". Or, you could have an array with one element, where that element is a zero: my @array = (0);
my @array = (); should work just fine -- it allocates a new array called @array, and then assigns it the empty list, (). Note that this is identical to simply saying my @array;, since the initial value of a new array is the empty list anyway.
Are you sure you are getting an error from this line, and not somewhere else in your code? Ensure you have use strict; use warnings; in your module or script, and check the line number of the error you get. (Posting some contextual code here might help, too.)
my @arr2=(0) x $#arr1 as well, no?$array[$i]++ from an empty array, things will "just work".$#arr1 is not the same as scalar(@arr1). For an array with five elements, the former is 4 and the latter is 5 (assuming you haven't altered $[ from its default).To produce the output in your comment to your post, this will do it:
use strict;
use warnings;
my @other_array = (0,0,0,1,2,2,3,3,3,4);
my @array;
my %uniqs;
$uniqs{$_}++ for @other_array;
foreach (keys %uniqs) { $array[$_]=$uniqs{$_} }
print "array[$_] = $array[$_]\n" for (0..$#array);
Output:
array[0] = 3
array[1] = 1
array[2] = 2
array[3] = 3
array[4] = 1
This is different than your stated algorithm of producing a parallel array with zero values, but it is a more Perly way of doing it...
If you must have a parallel array that is the same size as your first array with the elements initialized to 0, this statement will dynamically do it: @array=(0) x scalar(@other_array); but really, you don't need to do that.
$arr[i] += 1;can be better in some cases,++has some magic in Perl that causes it to be a bit slower.