How can I reference a specific row(s) in a data frame using an instance of a column variable in r? : <p>Lets say I have the following data frame in r:</p>

<pre><code>&gt; patientData
        patientID age diabetes    status
      1         1  25   Type 1      Poor
      2         2  34   Type 2  Improved
      3         3  28   Type 1 Excellent
      4         4  52   Type 1      Poor
</code></pre>

<p>How can I reference a specific row or group of rows by using the specific value/level of a particular column rather than the row index?  For instance, if I wanted to set a variable x to equal all of the rows which contain a patient with Type 1 diabetes or all of the rows that contain a patient in "Improved" status, how would I do that?</p>
