title: Concat values of array with same key
body: <p>I want to concat values of array with same key
  Example:</p>
  
  <pre><code>[0] =&gt; Array
          (
              [0] =&gt; A
              [1] =&gt; XYZ
          )
  
  [1] =&gt; Array
      (
          [0] =&gt; B
          [1] =&gt; ABC
      )
  
  [2] =&gt; Array
      (
          [0] =&gt; A
          [1] =&gt; LMN
      )
  
  [3] =&gt; Array
      (
          [0] =&gt; B
          [1] =&gt; PQR
      )
  )
  </code></pre>
  
  <p>Expected output:</p>
  
  <pre><code>[0] =&gt; Array
          (
              [0] =&gt; A
              [1] =&gt; XYZ,LMN
          )
  
  [1] =&gt; Array
      (
          [0] =&gt; B
          [1] =&gt; ABC,PQR
      )
  )
  </code></pre>