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.error { color:#AA0000; }</style></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><div class="bloop_markdown"><p>Hi Tom,<br>
It has been fixed in 1.9.3, <a href="https://github.com/Rdatatable/data.table/issues/481">bug#481</a>. You can scroll down the <a href="https://github.com/Rdatatable/data.table">project page</a> on instructions for installation..</p>
<p>Best,
</p></div><div class="bloop_original_html"><style>body{font-family:Helvetica,Arial;font-size:13px}</style><div id="bloop_customfont" style="font-family:Helvetica,Arial;font-size:13px; color: rgba(0,0,0,1.0); margin: 0px; line-height: auto;"><br></div> <div id="bloop_sign_1407152458412420864" class="bloop_sign"><div style="font-family:helvetica,arial;font-size:13px">Arun</div></div> <div style="color:black"><br>From: <span style="color:black">Tom Harrop</span> <a href="mailto:thomas.harrop@ird.fr"><thomas.harrop@ird.fr></a><br>Reply: <span style="color:black">Tom Harrop</span> <a href="mailto:thomas.harrop@ird.fr"><thomas.harrop@ird.fr>></a><br>Date: <span style="color:black">August 4, 2014 at 1:40:32 PM</span><br>To: <span style="color:black">datatable-help@lists.r-forge.r-project.org</span> <a href="mailto:datatable-help@lists.r-forge.r-project.org"><datatable-help@lists.r-forge.r-project.org>></a><br>Subject: <span style="color:black"> [datatable-help] Unexpected behaviour using fast grouping <br></span></div><br> <blockquote type="cite" class="clean_bq"><span><div><div></div><div>Hello,
<br>
<br>I'm trying to group a data.table that has duplicate keys, aggregating
<br>the values in another column by the value of the key.
<br>
<br>There is a question and answer on the same topic on StackOverflow
<br>(http://stackoverflow.com/a/17033371/3017012), but when I follow the
<br>accepted answer I get different results:
<br>
<br> > library(data.table)
<br>data.table 1.9.2 For help type: help("data.table")
<br> > dt = data.table(user_id = c(1,2,2,3), advertiser_id = c(1:4))
<br> > dt[,list(list(advertiser_id)), by = user_id]
<br> user_id V1
<br>1: 1 4,3
<br>2: 2 4,3
<br>3: 3 4,3
<br>
<br>Where I expect:
<br>
<br> user_id V1
<br>1: 1 1
<br>2: 2 2,3
<br>3: 3 4
<br>
<br>I can get the expected results (as above) using:
<br>
<br> > dt[,paste(advertiser_id, collapse = ","), by = user_id]
<br>
<br>Have I missed something? I'm on R 3.1.1 in case the behaviour has
<br>changed recently.
<br>
<br>Many thanks,
<br>
<br>Tom
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<br></div></div></span></blockquote></div><div class="bloop_markdown"><p></p></div></body></html>