@{$array[$i]} = map {0} (1..3);
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For those who, like me, were puzzled about the idea of using 'x' in a list context, check out the 'perlop' manpage:

Binary "x" is the repetition operator. In scalar context, it returns a string consisting of the left operand repeated the number of times specified by the right operand. In list context, if the left operand is a list in parentheses, it repeats the list.

           @ones = (1) x 80;           # a list of 80 1's
           @ones = (5) x @ones;        # set all elements to 5
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---
-DA
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This does what you want in a one liner. The loop is a little easier to understand if you are unfamiliar with map but they are essentially identical.

I have also shown you how to make your data access a lot less rigid. This code does not care about the structure of your 2D array which has been made irregular.

Not sure what you mean by access a 2D array as 1D. Do you want to flatten it into a list? I have coded that for you. Otherwise it is a 2D structure.

tachyon

#!/usr/bin/perl -w

use strict; 

# here we have an irregular sized 2D array
my @array = ( [1],[2,2],[3,3,3],[4,4,4,4] );
my $all ='42';

# this sets all elements to $all
for (@array) {
  @$_ = ($all) x @$_;
}

# this also sets all elements to $all
# map is just the loop above in short form 
map{ @$_ = ($all) x @$_ }@array;

# this prints the entire structure
for (@array) {
  for (@$_) {
      print "-",$_;
  }
  print"\n";
}
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Explanation. $_ is magical. When we loop over @array each element is aliased to $_ in turn if we modify $_ we modify the actual element @$_ derefs our array elements in list context and allows us to modify them @$_ in scalar context gives the number of elements thus the polymorphic behaviour in this example

If you want to flatten this 2D array into a 1D array this code does that

map{ push @list, @$_ }@array;
print "@list";
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sub ar_init {
        (defined $_[1])
                ? [ map { ar_init(@_) } (1..shift()) ]
                : shift() ;
}

my $r_array = ar_init(3,3,'-');
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But I'll be the first to admit that it might be clearer for future maintainers if you just use for loops!

Andy.
update: tiny simplification

small addendum to previous post

on the subject of maintainability this is really bad!
but is does print out entire 2D array in one line :-)

my @array = ( [1],[2,2],[3,3,3],[4,4,4,4] );
map{map{print "-",$_}@$_;print"\n"}@array;
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This code would almost pass for a JAPH now! In fact here is a challenge. Here is some code based on this thread. What does this do, no running it now, that would be cheating ;-)

my@a=([],[],[],[],[],[],[],[],[],[]);
my$a=-1;map{@$_=(++$a)x$a}@a;
map{map{print "-",$_}@$_;print"\n"}@a;
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tachyon