title: problems with data.table lapply(.SD)
body: <p><code>data.table</code> used to powerfully allow combinations of <code>.SDcols</code> and <code>lapply(.SD, foo)</code> within the <code>j</code> of <code>dt[i,j,...]</code>. Now it doesn't seem to. Has the proper syntax changed? Is the operation no longer supported? Any help would be greatly appreciated!</p>
  
  <p>example below:</p>
  
  <pre><code>library(data.table)
  set.seed(1234L)
  dt &lt;- data.table(matrix(rnorm(1e5), ncol= 20))
  
  # This used to work fine , now it returns 0 rows
  dt &lt;- dt[, lapply(.SD, floor), .SDcols= c(3:6, 15:20), with=FALSE]
  # Once that stopped, this worked as substitute
  # now it gives the below error
  dt[,c(3:6, 15:20), with=FALSE] &lt;- dt[,c(3:6, 15:20), with=FALSE][,lapply(.SD, floor)]
  </code></pre>
  
  <blockquote>
    <p>Error in <code>[&lt;-.data.table</code>(<code>*tmp*</code>, , c(3:6, 15:20), with = FALSE, value = list( : 
      unused argument (with = FALSE)</p>
  </blockquote>
  
  <pre><code>R&gt; sessionInfo()
  R version 3.3.2 (2016-10-31)
  Platform: x86_64-apple-darwin13.4.0 (64-bit)
  Running under: macOS Sierra 10.12.4
  # also fails on: Running under: CentOS Linux 7 (Core)
  
  locale:
  [1] en_US.UTF-8/en_US.UTF-8/en_US.UTF-8/C/en_US.UTF-8/en_US.UTF-8
  
  attached base packages:
  [1] stats     graphics  grDevices utils     datasets  methods   base     
  
  other attached packages:
  [1] data.table_1.10.4
  
  loaded via a namespace (and not attached):
  [1] tools_3.3.2
  </code></pre>
  
  <p>Cross reported on <a href="https://github.com/Rdatatable/data.table/issues/2221" rel="nofollow noreferrer">github/data.table</a></p>