Array initialization in Perl

Question

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

User · Accepted Answer

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       gt   tallies     n  for sort   a  lt   gt   b  keys  tallies        Output   0   gt  3 1   gt  1 2   gt  2 3   gt  3 4   gt  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

User · Answer

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

User · Answer

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

[perl] Array initialization in Perl

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