title: Subset and replace rows and columns in a data.table
body: <p>I need to modify certain columns of specific rows of a data.table. I keep getting an error, "unused argument (with=F)". Does anyone know how to quickly deal with this?  Below is an example using both data.frames and data.table.</p>
  
  <p>Thanks.</p>
  
  <pre><code>     test.df &lt;- data.frame(a=rnorm(100, 0, 1), b=rnorm(100, 0, 1), c=rnorm(100,0,1))
       test.dt &lt;- as.data.table(test.df)
  
       test.df[test.df$a&lt;test.df$b,c(1,2)] &lt;- 10* test.df[test.df$a&lt;test.df$b,c(1,2)]
  
       test.dt[test.dt$a&lt;test.dt$b, c(1,2), with=F] &lt;- 10* test.dt[,c(1,2),with=F][test.dt$a&lt;test.dt$b, c(1,2), with=F]
  </code></pre>