title: PHP - Array mapping or filtering
body: <p>Sorry for the vague title, I had trouble summarizing this question in one sentence (I'm open to suggestions or edits).</p>
  
  <p>I have a 2 dimensional associative array with an array of 2 numbers for each key.</p>
  
  <p>Like this:</p>
  
  <pre><code>Array
     (
     [one] =&gt; Array
        (
        [0] =&gt; 1
        [1] =&gt; 2
     )
     [two] =&gt; Array
        (
        [0] =&gt; 1
        [1] =&gt; 2
     )
     [three] =&gt; Array
        (
        [0] =&gt; 1
        [1] =&gt; 2
     )
  )
  </code></pre>
  
  <p>I'm wondering if there is a way to use array_map() or array_filter() to return an array that has each key and the first number in each of the value arrays, like this:</p>
  
  <pre><code>Array
     (
     [one] =&gt; 1
     [two] =&gt; 1
     [three] =&gt; 1
  )
  </code></pre>
  
  <p>I do not wish to create a new array by using a loop or anything like that, I'd like to do the conversion on the fly as an argument to a function, if you know what I mean.</p>
  
  <p>I could write my own function to achieve this but I'm interested in knowing if it can be done with array_map() or array_filter().</p>
  
  <p>I tried using various combinations of array_merge(), array_keys() and array_values() with no success.</p>
  
  <p>I thank you in advance for any help you may provide.</p>