title: r replace character values in a column with the lowest numeric value of that column
body: <p>I have a data frame where some of the values in some of the columns are entered as 'L' (for too low to measure), and the rest of the values are numeric. I'd like to replace the 'Low' with the lowest numeric value within the column: </p>
  
  <p>What I have:</p>
  
  <pre><code>A   4   6   5   L
  B   4   L   9   3
  C   6   7   6   5
  D   L   8   L   3
  </code></pre>
  
  <p>What I'd like:              </p>
  
  <pre><code>A   4   6   5   3
  B   4   6   9   3
  C   6   7   6   5
  D   4   8   5   3
  </code></pre>
  
  <p>I've gone down a complicated road, generating a look-up table, and then trying to apply that over all the columns in the data frame and I keep thinking there's got to be an easier way.</p>
  
  <p>Any help is appreciated! Thank you-</p>