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<p class="MsoNormal">I’m running into an issue where a data.table has a column with the same name as a variable, and I would like to reference the variable in an i expression.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">For example,<o:p></o:p></p>
<p class="MsoNormal"><span style="font-family:"Courier New""><o:p> </o:p></span></p>
<p class="MsoNormal" style="margin-left:.5in"><span style="font-family:"Courier New"">library(data.table)<o:p></o:p></span></p>
<p class="MsoNormal" style="margin-left:.5in"><span style="font-family:"Courier New""><o:p> </o:p></span></p>
<p class="MsoNormal" style="margin-left:.5in"><span style="font-family:"Courier New"">x <- data.table(y = 1:10, z = 11:20)<o:p></o:p></span></p>
<p class="MsoNormal" style="margin-left:.5in"><span style="font-family:"Courier New"">setkey(x, y)<o:p></o:p></span></p>
<p class="MsoNormal" style="margin-left:.5in"><span style="font-family:"Courier New""><o:p> </o:p></span></p>
<p class="MsoNormal" style="margin-left:.5in"><span style="font-family:"Courier New"">z <- data.table(y = 1:5, w = 21:25)<o:p></o:p></span></p>
<p class="MsoNormal" style="margin-left:.5in"><span style="font-family:"Courier New"">setkey(z, y)<o:p></o:p></span></p>
<p class="MsoNormal"><b><span style="font-size:10.0pt"><o:p> </o:p></span></b></p>
<p class="MsoNormal">I want to extract the subset of x with values of y that are not in the y column of the data.table z. I can do the following:<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal" style="margin-left:.5in"><span style="font-family:"Courier New"">ind <- setdiff(x[,y], z[,y])<o:p></o:p></span></p>
<p class="MsoNormal" style="margin-left:.5in"><span style="font-family:"Courier New"">x[ind]<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New""><o:p> </o:p></span></p>
<p class="MsoNormal">But I can’t do the following:<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal" style="margin-left:.5in"><span style="font-family:"Courier New"">x[setdiff(y, z[,y])]<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New""><o:p> </o:p></span></p>
<p class="MsoNormal">because it tries to use the column z instead of the data.table z. Is there any way to get around that? I tried using “with = FALSE”, but that only seems to apply to the j expression.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Thank you for your help.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">- Elliot<o:p></o:p></p>
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