This here is a simple implementation of what you are asking for. Note that I renamed your data.table from "a" to "DT" and that I changed the first value of b to 0.5, so that one can easily check if the index generation is working:<div>
<br></div><div><div>DT <- data.table(year = 2001:2010, </div><div> b = c(0.5, 2:10), </div><div> c = 11:20, </div><div> d = 21:30)</div><div><br></div><div>DT[, db := d/b]</div>
<div>DT[, cb := c/b]</div><div>DT[, index_b := b/b[1]]</div><div>DT[, index_c := c/b[1]]</div><div><br></div><div>So basically, I just use the := operator all the time, which is a handy feature. You can check out the help page by typing <span style="color:rgb(127,0,85);font-family:'Lucida Console';font-size:9pt;line-height:1.3;white-space:pre-wrap;text-align:-webkit-left">?':=' </span>in the R console.</div>
<div><br></div><div>Does this would you want to do? Or were you looking for a more automatic way of doing this? If so, it would help if you would be more specific about how your real use case looks like.</div><div><br></div>
<div>
Christoph</div></div><br><div class="gmail_quote">On Mon, Jan 16, 2012 at 3:38 PM, Serdar Akin <span dir="ltr"><<a href="mailto:serdar.akin@pensionsmyndigheten.se" target="_blank">serdar.akin@pensionsmyndigheten.se</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
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<font face="Verdana"><span style="font-size:9pt">
<div>Hi,</div>
<div> </div>
<div>I have a problem that I want to divide column “b” with all the other columns, in this case “c” and “d” , is there a nice way to do this?</div>
<div> </div>
<div>Further I would like to divide columns “b,c,d” with row 1 form column “b” to create a index?</div>
<div> </div>
<div><font face="Calibri"><span style="font-size:11pt"> </span></font></div>
<div>a <- data.table(year = 2001:2010, b = 1:10, c = 11:20, d = 21:30)</div>
<div><font face="Calibri"><span style="font-size:11pt"> </span></font></div>
<div><font face="Calibri"><span style="font-size:11pt"> </span></font></div>
<div style="margin-bottom:10pt">Regards Serdar</div>
<div><font face="Calibri"><span style="font-size:11pt"> </span></font></div>
<div><font face="Calibri"><span style="font-size:11pt"> </span></font></div>
</span></font>
</div>
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