title: How to change a column classed as NULL to class integer?
body: <p>So I'm starting with a dataframe called max.mins that has 153 rows.</p>
  
  <pre><code>    day  Tx      Hx      Tn
  1   1   10.0    7.83    2.1
  2   2   7.7     6.19    2.5
  3   3   7.1     4.86    0.0
  4   4   9.8     7.37    2.7
  5   5   13.4    12.68   0.4
  6   6   17.5    17.47   3.5
  7   7   16.5    15.58   6.5
  8   8   21.5    20.30   6.2
  9   9   21.7    21.41   9.7
  10  10  24.4    28.18   8.0
  </code></pre>
  
  <p>I'm applying these statements to the dataframe to look for specific criteria</p>
  
  <pre><code>temp_warnings &lt;- subset(max.mins, Tx &gt;= 32 &amp; Tn &gt;=20)
  humidex_warnings &lt;- subset(max.mins, Hx &gt;= 40)
  </code></pre>
  
  <p>Now when I open up humidex_warnings for example I have this dataframe</p>
  
  <pre><code>   row.names    day    Tx     Hx     Tn
  1   41          10    31.1  40.51   20.7
  2   56          25    33.4  42.53   19.6
  3   72          11    34.1  40.78   18.1
  4   73          12    33.8  40.18   18.8
  5   74          13    34.1  41.10   22.4
  6   79          18    30.3  41.57   22.5
  7   94           2    31.4  40.81   20.3
  8   96           4    30.7  40.39   20.2
  </code></pre>
  
  <p>The next step is to search for 2 or 3 consective numbers in the column row.names and give me a total of how many times this occurs (I asked this in a previous question and have a function that should work once this problem is sorted out). The issue is that row.names is class NULL which is preventing me from applying further functions to this dataframe.</p>
  
  <p>Help? :)</p>
  
  <p>Thanks in advance,
  Nick</p>