title: Summing many columns with data.table in R, remove NA
body: <p>This is really two questions I guess. I'm trying to use the data.table package to summarize a large dataset. Say my original large dataset is df1 and unfortunately df1 has 50 columns (y0... y49) that I want the sum of by 3 fields (segmentfield1, segmentfield2, segmentfield3). Is there a simpler way to do this than typing every y0...y49 column out? Related to this, is there a generic na.rm=T for the data.table instead of typing that with each sum too?</p>
  
  <pre><code>dt1 &lt;- data.table(df1)
  setkey(dt1, segmentfield1, segmentfield2, segmentfield3)
  dt2 &lt;- dt1[,list( y0=sum(y0,na.rm=T), y1=sum(y1,na.rm=T), y2=sum(y2,na.rm=T), ... 
              y49=sum(y49,na.rm=T) ),
              by=list(segmentfield1, segmentfield2, segmentfield3)]
  </code></pre>