title: How to use the Spread function using only one value of the target column?
body: <p>We have the following data frame <code>a</code> with something like this:</p>
  
  <pre class="lang-r prettyprint-override"><code>
   &gt; a
      google_prod      Value
  1     categoria          ML
  2        google         120
  3       youtube          24
  4     categoria          AO
  5        google           2
  6       youtube           0
  7     categoria          ML
  8        google          27
  9       youtube           0
  10    categoria          AO
  11       google           5
  12      youtube           0
  </code></pre>
  
  <p>We would like to get this:</p>
  
  <pre class="lang-r prettyprint-override"><code>    categoria google_prod    Value
  1          ML   google        120
  2          ML   youtube        24
  3          AO   google          2
  4          AO   youtube         0      
  5          ML   google         27
  6          ML   youtube         0    
  7          AO   google          5
  8          AO    youtube        0    
  </code></pre>
  
  <p>In other words, perform a type of application of the Spread or similar function, where only one value is taken from the google_prod column to apply it, in this case it would be the 'categoria' value.</p>