<div>How about this?</div><div>
for (j in v) set(dt, i=NULL, j=j, dt[[j]]*dt[[coeff]])
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<div><div><br></div><div>Arun</div><div><br></div></div>
<p style="color: #A0A0A8;">On Sunday, October 27, 2013 at 9:37 AM, cduprez wrote:</p>
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<span><div><div><div>Hi all,</div><div><br></div><div>I am trying to update columns of a data.table, whose names are in a vector,</div><div>by multiplicating their values with the values of another column (whose name</div><div>is in another vector).</div><div>Example : </div><div>dt <- data.table(a=c(1, 1, 1, 1, 1), b=c(2, 2, 2, 2, 2), c=c(3, 3, 3, 3, 3),</div><div>d=c(4, 4, 4, 4, 4), e=c(5, 5, 5, 5, 5), coef = c(1, 2, 3, 4, 5))</div><div>v <- c("b", "c")</div><div>coef <- c("coef")</div><div><br></div><div>dt</div><div> a b c d e coef</div><div>1: 1 2 3 4 5 1</div><div>2: 1 2 3 4 5 2</div><div>3: 1 2 3 4 5 3</div><div>4: 1 2 3 4 5 4</div><div>5: 1 2 3 4 5 5</div><div><br></div><div>And what I am looking for, as result, is : b = b*coef, c = c*coef</div><div> a b c d e coef</div><div>1: 1 2 3 4 5 1</div><div>2: 1 4 6 4 5 2</div><div>3: 1 6 9 4 5 3</div><div>4: 1 8 12 4 5 4</div><div>5: 1 10 15 4 5 5</div><div><br></div><div>How can I compute that result by keeping the columns to update and the coef</div><div>column in character vectors containing the columns names.</div><div>I precise that the coef vector still contains only one column name.</div><div><br></div><div>Thanks in advance for you help.</div><div><br></div><div>Regards,</div><div><br></div><div>Cedric</div><div><br></div><div><br></div><div><br></div><div>--</div><div>View this message in context: <a href="http://r.789695.n4.nabble.com/Update-data-table-columns-by-multiplication-of-another-column-tp4679124.html">http://r.789695.n4.nabble.com/Update-data-table-columns-by-multiplication-of-another-column-tp4679124.html</a></div><div>Sent from the datatable-help mailing list archive at <a href="http://Nabble.com">Nabble.com</a>.</div><div>_______________________________________________</div><div>datatable-help mailing list</div><div><a href="mailto:datatable-help@lists.r-forge.r-project.org">datatable-help@lists.r-forge.r-project.org</a></div><div><a href="https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/datatable-help">https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/datatable-help</a></div></div></div></span>
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