title: Filtering data frame with Matrix column in R
body: <p>I have a very simple data frame that has a ID column and a column that indicates if the row was a true positive or not (either 1 or 0). I aggregated the data by ID using plyr's each function and calculated the number of occurrences for the ID and the mean value for true positive using<code>agg &lt;- aggregate(tp ~ v_id, data, each(mean, length))</code>
  That seemed to have worked well and I got the following data:</p>
  
  <pre><code>head(agg)
                  v_id tp.mean tp.length
  1             A51599     1.0         4
  2             A51670     1.0         2
  3             A51672     1.0         2
  4             A51676     1.0         2
  5             A51677     1.0         2
  6             A51678     0.5         2
  </code></pre>
  
  <p>That data is nice, but now I would like to filter out all rows where the tp.length is less than 100. I tried all kinds of things with the subset function as well with the '[]' operator with conditions in it. The tp column seems to be a matrix and I have no idea, how to get to the tp.length in the filter.</p>
  
  <p>Thank you!</p>