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    <div class="moz-cite-prefix">Or a slight refinement of that:<br>
      <br>
      system.time(out2 <- data.table(id=seq(vec2), val=vec2,
      key="val")[J(vec1), list(list(id))]$V1)<br>
      <br>
      Matthew<br>
      <br>
      On 25/08/13 21:58, Arunkumar Srinivasan wrote:<br>
    </div>
    <blockquote cite="mid:9697748E77C14BBB8FFF82B5A905F2DC@gmail.com"
      type="cite">
      <div>
        <div>How about this?
          <div><br>
          </div>
          <div>system.time(out <- data.table(id=seq(vec2), val=vec2,
            key="val")[J(vec1)][, list(list(id)), by=val]$V1)</div>
          <div>
            <div>   user  system elapsed </div>
            <div>  0.098   0.004   0.103 </div>
          </div>
        </div>
      </div>
      <div>
        <div><br>
        </div>
        <div>Arun</div>
        <div><br>
        </div>
      </div>
      <p style="color: #A0A0A8;">On Sunday, August 25, 2013 at 10:27 PM,
        arun wrote:</p>
      <blockquote type="cite"
style="border-left-style:solid;border-width:1px;margin-left:0px;padding-left:10px;">
        <span>
          <div>
            <div>
              <div>Hi,</div>
              <div>I tried a ?data.table() method to solve the problem
                in the link below.  </div>
              <div><br>
              </div>
              <div><a moz-do-not-send="true"
href="http://r.789695.n4.nabble.com/how-to-combine-apply-and-which-or-alternative-ways-to-do-so-td4674424.html#a4674434">http://r.789695.n4.nabble.com/how-to-combine-apply-and-which-or-alternative-ways-to-do-so-td4674424.html#a4674434</a></div>
              <div><br>
              </div>
              <div>But, it was not that fast.</div>
              <div><br>
              </div>
              <div>set.seed(24)</div>
              <div>vec1<- sample(1e5,1e3,replace=FALSE)</div>
              <div>set.seed(48)</div>
              <div>vec2<- sample(1e3,1e6,replace=TRUE)</div>
              <div>system.time({res1<-
                tapply(vec1,1:1e3,FUN=function(i) {which(vec2==i)})})
#
                user  system elapsed </div>
              <div>#  3.912   0.000   3.880 </div>
              <div><br>
              </div>
              <div>system.time(res2<- sapply(vec1,function(x)
                which(vec2%in%x)))</div>
              <div>#   user  system elapsed </div>
              <div># 24.368   0.000  23.247 </div>
              <div>
vecR1<-unlist(res1)</div>
              <div>names(vecR1)<-NULL</div>
              <div>vecR2<- unlist(res2)</div>
              <div>identical(vecR1,vecR2)</div>
              <div>#[1]TRUE</div>
              <div><br>
              </div>
              <div>library(data.table)</div>
              <div>dt1<- data.table(vec1,Group=1:1e3,key='Group')</div>
              <div>system.time({res3<-
                dt1[,list(list(which(vec1==vec2))),by=Group]})##Not that
                fast
</div>
              <div># user  system elapsed </div>
              <div>#  3.756   0.120   3.886 ######</div>
              <div>identical(vecR1,unlist(res3$V1))</div>
              <div>#[1] TRUE</div>
              <div><br>
              </div>
              <div><br>
              </div>
              <div><br>
              </div>
              <div>Is there a faster way?</div>
              <div><br>
              </div>
              <div>Thanks.</div>
              <div><br>
              </div>
              <div>A.K.</div>
              <div>_______________________________________________</div>
              <div>datatable-help mailing list</div>
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                  href="mailto:datatable-help@lists.r-forge.r-project.org">datatable-help@lists.r-forge.r-project.org</a></div>
              <div><a moz-do-not-send="true"
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> </blockquote>
      <div> <br>
      </div>
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