title: Fast replacing values in dataframe in R
body: <p>I have a dataframe of 150,000 rows with 2,000 columns containing values, some being negatives. 
  I am replacing those negative values by 0, but it is extremely slow to do so (~60min or more). </p>
  
  <p><code>df[df   &lt; 0] = 0</code></p>
  
  <p>where <code>df[,1441:1453]</code> looks like (all columns/values numeric):</p>
  
  <pre><code>  V1441 V1442 V1443 V1444 V1445 V1446 V1447 V1448 V1449 V1450 V1451 V1452 V1453
  1     3     1     0     4     4    -2     0     3    12     5    17    34    27
  2     0     1     0     7     0     0     0     1     0     0     0     0     0
  3     0     2     0     1     2     3     6     1     2     1    -6     3     1
  4     1     2     3     6     1     2     1    -6     3     1    -4     1     0
  5     1     2     1    -6     3     1    -4     1     0     0     1     0     0
  6     1     0     0     1     0     0     0     0     0     0     1     2     2
  </code></pre>
  
  <p>Is there a way to speed up such process, eg the way I am doing it is utterly slow, and there is faster approach for this ? 
  Thanks.</p>