title: Extract a grid from a one-dimentional array
body: <p>I have an array with 12 values and I need to display these in a grid like this (always 4 columns, 3 rows):</p>
  
  <pre><code>  1  |  2  |  3  |  4
   ----------------------
    5  |  6  |  7  |  8
   ----------------------
    9  |  10 |  11 |  12
  </code></pre>
  
  <p>I am looping through the <strong>grid</strong> and I have two coordinates: column and row.</p>
  
  <p>How do I know which index belongs to which row and column? I tried several things, but they are not working:</p>
  
  <pre><code>objectAtIndex: (row + 1) * (column + 1) - 1
  objectAtIndex: row + column
  </code></pre>
  
  <p>etc...</p>
  
  <hr>
  
  <p>Row and column indexes start with 0.</p>