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<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Dear Data Table Help List,<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I am using data.table version 1.6 (with R version 2.13.0, 64-bit on Windows 7) and I’ve come across some strange behavior.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Please look at the following example, where I simply take the mean of two numbers.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><span style="font-family:"Courier New"">> table1 <- data.table(A=c("a","b","b"),B=c(4,5,NA))<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New"">> setkey(table1,A)<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New"">> table1["b",mean(B,na.rm=T)]<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New""> A V1<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New"">[1,] b 5<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New";color:#00B050"># EXPECTED OUTPUT<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New""><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New"">> table2 <- data.table(A=c("a","b","b"),B=c(4,5,NA))<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New"">> table2[A=="b",mean(B,na.rm=TRUE)]<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New"">[1] 5<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New";color:#00B050"># LESS EFFICIENT, BUT EXPECTED OUTPUT<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New""><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New"">> table2[A=="b",mean(B,na.rm=T)]<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New"">Error in `[.data.table`(x, irows, all.vars(jsub), with = FALSE) :
<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New""> undefined columns selected<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New";color:red"># WHY THE ERROR?<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New";color:red"><o:p> </o:p></span></p>
<p class="MsoNormal">Any help would be much appreciated.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Regards,<o:p></o:p></p>
<p class="MsoNormal">Alex<o:p></o:p></p>
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