johnvandam has asked for the wisdom of the Perl Monks concerning the following question:

Call me silly, but I'm frustrated a bit with the following:
I would like to make an array of say, a thousand elements each filled with 0. What would be the fastest, cleanest way of doing this?

For a string we can replicate a substring:

$string = 0 x 1000;

This will give me a string of a thousand 0's.

For making an array in similar fashion this is the shortest method I can think of:

$_ = 0 foreach (@array = (1..1000));

I could also use split:

@array = split //, 0 x 1000;

But this I think will be more costly because you invoke the regexp engine, I guess.

So my question is: Is there some infinitely better, more perly method of making an array of predefined length with identical values? (Comparable maybe to the more satisfying way of doing something similar for a string?)

Thanks for all the help!

Replies are listed 'Best First'.
Re: Making an array of predifined length with default values
by almut (Canon) on Mar 04, 2009 at 11:53 UTC 
    my @array = (0) x 1000;

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    Even works with lists of arbitrary length, such as my @array = (1, 2, 3) x 100;  (which creates 300 elements).

    (but memory-wise, it's not better than iteratively filling the elements, maybe even with predeclaring some initial max size with $#array = 1000; to avoid successive automatic resizing...)

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      Just a very minor nit: the statement  $#array = 1000; sets the maximum array index to 1000 and so predeclares an array with 1001 elements (assuming $[ == 0; see perlvar).
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      Thanks, this works perfectly! I though it only worked for strings. Thanks again
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Re: Making an array of predifined length with default values
by derby (Abbot) on Mar 04, 2009 at 11:54 UTC

    The fastest way to pre-extend an array by assigning a value to it's length: 

    my @array;
$#array = 10000;

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    Now for pre-filling ... don't know. I would Benchmark the approaches you outline (and for grins, I would benchmark pre-extending too).

    -derby

    Update: Doh!. Thanks almut, now I know.

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Re: Making an array of predifined length with default values
by clueless newbie (Curate) on Mar 04, 2009 at 11:59 UTC
    perhaps @a=(0) x 1000;
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