title: Return row number(s) for a particular value in a column in a dataframe
body: <p>I have a data frame <code>(df)</code> and I was wondering how to return the row number(s) for a particular value <code>(2585)</code> in the <code>4th column (height_chad1)</code> of the same data frame? </p>
  
  <p>I've tried: </p>
  
  <pre><code>row(mydata_2$height_chad1, 2585)
  </code></pre>
  
  <p>and <strong>I get the following error:</strong></p>
  
  <pre><code>Error in factor(.Internal(row(dim(x))), labels = labs) : 
    a matrix-like object is required as argument to 'row'
  </code></pre>
  
  <p>Is there an equivalent line of code that works for data frames instead of matrix-like objects?</p>
  
  <p>Any help would be appreciated. </p>