<html xmlns:v="urn:schemas-microsoft-com:vml" xmlns:o="urn:schemas-microsoft-com:office:office" xmlns:w="urn:schemas-microsoft-com:office:word" xmlns:m="http://schemas.microsoft.com/office/2004/12/omml" xmlns="http://www.w3.org/TR/REC-html40"><head><meta http-equiv=Content-Type content="text/html; charset=us-ascii"><meta name=Generator content="Microsoft Word 12 (filtered medium)"><style><!--
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</o:shapelayout></xml><![endif]--></head><body lang=EN-US link=blue vlink=purple><div class=WordSection1><p class=MsoNormal>All,<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>I’m curious from a speed perspective what the analog of apply is in data.table as I have a problem where, for each row, I want to take either the min or the max of several columns depending upon the value of a third column:<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><o:p> </o:p></p><p class=MsoNormal>test.dt <- data.table(ID=1:10, SCORE_1=rnorm(10), SCORE_2=rnorm(10), SCORE_3=rnorm(10), MAX_OR_MIN=c(rep("Max", 5), rep("Min", 5)))<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>For each row I’d like to get the max of SCORE_1, SCORE_2, and SCORE_3 if the MAX_OR_MIN value is MAX and the min of SCORE_1, SCORE_2, and SCORE_3 if the MAX_OR_MIN value is MIN. <o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>It isn’t too difficult to come up with a “bulky” and slow solution, but I’m wondering if I’m missing a way in which data.table would make such an effort elegant and quick.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Any help greatly appreciated. <o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Damian Betebenner<span style='color:navy'><o:p></o:p></span></p><p class=MsoNormal>Center for Assessment<span style='color:navy'><o:p></o:p></span></p><p class=MsoNormal>PO Box 351<span style='color:navy'><o:p></o:p></span></p><p class=MsoNormal>Dover, NH 03821-0351<span style='color:navy'><o:p></o:p></span></p><p class=MsoNormal><span style='color:navy'> <o:p></o:p></span></p><p class=MsoNormal>Phone (office): (603) 516-7900<span style='color:navy'><o:p></o:p></span></p><p class=MsoNormal>Phone (cell): (857) 234-2474<span style='color:navy'><o:p></o:p></span></p><p class=MsoNormal>Fax: (603) 516-7910<span style='color:navy'><o:p></o:p></span></p><p class=MsoNormal><span style='color:navy'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:10.0pt;color:navy'><a href="mailto:dbetebenner@nciea.org">dbetebenner@nciea.org</a><o:p></o:p></span></p><p class=MsoNormal><span style='font-size:10.0pt;color:navy'><a href="http://www.nciea.org/">www.nciea.org</a><o:p></o:p></span></p><p class=MsoNormal><span style='font-size:10.0pt;color:navy'><o:p> </o:p></span></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><o:p> </o:p></p></div></body></html>