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Re: Initialize multi-dimensional array

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Thomas 'PointedEars' Lahn wrote:

> Andreas Bergmaier wrote:
>> var a=[];for(var i=0;i<2;i++){a[i]=[];for(var j=0;j<4;j++)a[i][j]=1;}
>         ^^                           ^^
> JFYI: You are using two Array literals here, of course.
>  
>> There might be tricky expressions with less code, but you don't really
>> want them.
> 
> A matter of opinion.  Surely
> 
>   var a = [];
>   a.length = 5;
>   a = a.join("1").split("").map(function (el) { return +el; });
>   a = [a, a.slice()];
> 
> is a more elegant solution to this problem.

It should be noted that this approach can also be used with multi-digit 
numbers and any other value:

  var a = [];
  a.length = 5;
  a = a.join(",12").split(",").map(function (el) { return +el; });
  a.shift();
  a = [a, a.slice()];

However more elegant, the map() method is not backwards compatible (so it 
requires comparably expensive emulation) and it is expensive itself because 
the function needs to be called multiple times.  Also, the need for 
additional shift() (or pop(), if you use "12," instead) with multi-character 
values reduces its elegance.

So a combination of the classical looping approach and the more elegant 
slicing approach (which performs the element assignment natively, therefore 
should be cheaper than an explicit loop) appears to be the best solution:

  function getFilledMatrix(rows, columns, fill)
  {
    var a = [];

    var tmp = [];
    tmp.length = columns;
    
    for (var j = 0; j < columns; ++j)
    {
      tmp[j] = fill || 0;
    }

    for (var i = 0; i < rows; ++i)
    {
      if (i == 0)
      {
        a.push(tmp);
      }
      else
      {
        a.push(tmp.slice());
      }
    }

    return a;
  }


PointedEars
-- 
When all you know is jQuery, every problem looks $(olvable).

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Thread

Initialize multi-dimensional array Archos <raul.san@sent.com> - 2012-01-24 15:09 -0800
  Re: Initialize multi-dimensional array Denis McMahon <denismfmcmahon@gmail.com> - 2012-01-25 09:56 +0000
  Re: Initialize multi-dimensional array Andreas Bergmaier <andber93@web.de> - 2012-01-25 11:48 +0100
    Re: Initialize multi-dimensional array Archos <raul.san@sent.com> - 2012-01-25 04:37 -0800
      Re: Initialize multi-dimensional array Richard Cornford <Richard@litotes.demon.co.uk> - 2012-01-25 06:35 -0800
    Re: Initialize multi-dimensional array Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-01-25 19:39 +0100
      Re: Initialize multi-dimensional array Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-01-28 01:42 +0100
  Re: Initialize multi-dimensional array "Michael Haufe (TNO)" <tno@thenewobjective.com> - 2012-01-25 09:38 -0800
  Re: Initialize multi-dimensional array Dr J R Stockton <reply1204@merlyn.demon.co.uk> - 2012-01-25 19:33 +0000
    Re: Initialize multi-dimensional array Ross McKay <au.org.zeta.at.rosko@invalid.invalid> - 2012-01-26 11:56 +1100
      Re: Initialize multi-dimensional array Dr J R Stockton <reply1204@merlyn.demon.co.uk> - 2012-01-27 20:09 +0000

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