title: sub setting a ff data frame using the subset.ff function in R
body: <p>Does anyone know how to use the <code>subset.ff</code> function in the <code>ff</code> package?</p>
  
  <p>Here is a sample of the data:</p>
  
  <pre><code>col1 col2 col3 col4 col5 col6 col7
      1    1    1    1    1    1    0
      1    1    1    1    1    1    0
    104   11    3    3    1    1 1089
     63   11    2    3    9    1  734
     11    1    3    1    1    1 -609
     11    1    3    1    1    1 -609
     11    1    3    1    1    1 -609
  </code></pre>
  
  <p>Here is the code:</p>
  
  <pre><code>temp2a &lt;- subset.ff(temp1,temp1$col7!="0") #temp1 is the name of the ff data frame
  </code></pre>
  
  <p>I get the following error:</p>
  
  <pre><code>Error in `length&lt;-.ffdf`(`*tmp*`, value = 12965531L) : not allowed to change the number of (virtual) columns of ffdf
  </code></pre>
  
  <p>I am trying to get two ff data frame subsets from the data. One where col7 is equal to 0 and one where col7 is not equal to zero. Does anyone know how to use the <code>subset.ff</code> function or another way to do what I want. I tried looking through the pdf for the <code>ffbase</code> library and all over the web but I couldn't find any examples.</p>
  
  <p>Cheers again,</p>
  
  <p>Lorcan</p>