<html>
  <head>
    <meta content="text/html; charset=ISO-8859-1"
      http-equiv="Content-Type">
  </head>
  <body bgcolor="#FFFFFF" text="#000000">
    <div class="moz-cite-prefix"><br>
      And more info here (see both answers) :<br>
<a class="moz-txt-link-freetext" href="http://stackoverflow.com/questions/10225098/understanding-exactly-when-a-data-table-is-a-reference-to-vs-a-copy-of-another">http://stackoverflow.com/questions/10225098/understanding-exactly-when-a-data-table-is-a-reference-to-vs-a-copy-of-another</a><br>
      <br>
      On 10/03/14 05:20, Michael Nelson wrote:<br>
    </div>
    <blockquote
      cite="mid:6FB5193A6CDCDF499486A833B7AFBDCDB81A54D9@ex-mbx-pro-05"
      type="cite">
      <meta http-equiv="Content-Type" content="text/html;
        charset=ISO-8859-1">
      <style type="text/css" id="owaParaStyle"></style>
      <div style="direction: ltr;font-family: Tahoma;color:
        #000000;font-size: 10pt;">This is well explained in the help
        file for `copy` (and `setnames`)
        <div><br>
        </div>
        <div>DT <- DT2 </div>
        <div><br>
        </div>
        <div>does *not* create a copy, it creates two object names that
          refer to the same object reference.</div>
        <div><br>
        </div>
        <div>If you want force the creation of a copy, use `copy`</div>
        <div><br>
        </div>
        <div>DT <- copy(DT2)</div>
        <div><br>
        </div>
        <div>Then your example will work as expected.</div>
        <div><br>
        </div>
        <div><br>
          <div style="font-family: Times New Roman; color: #000000;
            font-size: 16px">
            <hr tabindex="-1">
            <div id="divRpF47660" style="direction: ltr;"><font
                color="#000000" face="Tahoma" size="2"><b>From:</b>
                <a class="moz-txt-link-abbreviated" href="mailto:datatable-help-bounces@lists.r-forge.r-project.org">datatable-help-bounces@lists.r-forge.r-project.org</a>
                [<a class="moz-txt-link-abbreviated" href="mailto:datatable-help-bounces@lists.r-forge.r-project.org">datatable-help-bounces@lists.r-forge.r-project.org</a>] on
                behalf of Manabu Sakamoto [<a class="moz-txt-link-abbreviated" href="mailto:manabu.sakamoto@gmail.com">manabu.sakamoto@gmail.com</a>]<br>
                <b>Sent:</b> Monday, 10 March 2014 4:00 PM<br>
                <b>To:</b> <a class="moz-txt-link-abbreviated" href="mailto:datatable-help@lists.r-forge.r-project.org">datatable-help@lists.r-forge.r-project.org</a><br>
                <b>Subject:</b> [datatable-help] setnames on copy
                data.table also renames original data.table object<br>
              </font><br>
            </div>
            <div>
              <div dir="ltr">Dear list,
                <div><br>
                </div>
                <div>I have a data.table object for instance DT:</div>
                <div><br>
                </div>
                <div>x <- seq(1:100)</div>
                <div>y <- x^2</div>
                <div>DT <- data.table(X=x, Y=y)</div>
                <div><br>
                </div>
                <div>and I produce a copy</div>
                <div><br>
                </div>
                <div>DT2 <- DT</div>
                <div><br>
                </div>
                <div>which I rename</div>
                <div><br>
                </div>
                <div>setnames(DT2, c("A","B"))</div>
                <div><br>
                </div>
                <div>this somehow also renames DT, the names of which
                  are now "A" and "B".</div>
                <div><br>
                </div>
                <div>How can I just rename the copy and keep the names
                  of the original?</div>
                <div><br>
                </div>
                <div>Many thanks,</div>
                <div>Manabu<br clear="all">
                  <div><br>
                  </div>
                  -- <br>
                  <div dir="ltr">Manabu Sakamoto, PhD
                    <div><a moz-do-not-send="true"
                        href="mailto:manabu.sakamoto@gmail.com"
                        target="_blank">manabu.sakamoto@gmail.com</a></div>
                  </div>
                </div>
              </div>
            </div>
          </div>
        </div>
      </div>
      <br>
      <fieldset class="mimeAttachmentHeader"></fieldset>
      <br>
      <pre wrap="">_______________________________________________
datatable-help mailing list
<a class="moz-txt-link-abbreviated" href="mailto:datatable-help@lists.r-forge.r-project.org">datatable-help@lists.r-forge.r-project.org</a>
<a class="moz-txt-link-freetext" 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></pre>
    </blockquote>
    <br>
  </body>
</html>