<html><head></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><p><code>unique(Species)</code> is of length 3, where as the 2nd entry c(1.5, 2) is of length 2.</p>
<p><code>J</code> in <code>J(.)</code> is replaced with <code>list(.)</code> internally (using lazy evaluation), following which it’s converted to a <code>data.table</code> using <code>as.data.table(list(.))</code>. </p>
<p>And here your list is:</p>
<p><code>list(c("setosa", "versicolor", "virginica") , c(1.5, 2.0))</code> which results in the warning because it has to recycle to convert it to a data.table.</p>
<p>In the example you’ve linked, <code>J(.)</code> and <code>CJ(.)</code> will return the same result (because there’s just one value in 2nd column). So, the results don’t change. But the general expression is to use <code>CJ(.)</code> along with <code>nomatch=0L</code>, as you’ve done.</p>
<p>Those two expressions are equivalent, yes.</p>
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.error { color:#AA0000; }</style></p><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_1402847324782009088" 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">G See</span> <a href="mailto:gsee000@gmail.com">gsee000@gmail.com</a><br>Reply: <span style="color:black">G See</span> <a href="mailto:gsee000@gmail.com">gsee000@gmail.com</a><br>Date: <span style="color:black">June 15, 2014 at 5:45:11 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] subsetting by second key <br></span></div><br> <blockquote type="cite" class="clean_bq"><span><div><div></div><div>Hi,
<br>
<br>I want to subset a data.table using only its second key, which is
<br>demonstrated here
<br>http://stackoverflow.com/questions/15597685/subsetting-data-table-by-2nd-column-only-of-a-2-column-key-using-binary-search/15597713#15597713
<br>
<br>However, I need to subset with more than one value in the secondary key
<br>
<br>Is this warning expected? What exactly is it telling me?
<br>
<br> library(data.table)
<br> DT <- data.table(iris, key="Species,Petal.Width")
<br> DT[J(unique(Species), c(1.5, 2.0)), nomatch=0L]
<br> # Sepal.Length Sepal.Width Petal.Length Petal.Width Species
<br> #1: 6.0 2.2 5.0 1.5 virginica
<br> #2: 6.3 2.8 5.1 1.5 virginica
<br> #Warning message:
<br> #In as.data.table.list(i) :
<br> # Item 2 is of size 2 but maximum size is 3 (recycled leaving a
<br>remainder of 1 items)
<br>
<br>
<br>It looks like I can get what I want with either of these; can you
<br>confirm that both of these will always return the same result?
<br>
<br> DT[Petal.Width %in% c(1.5, 2.0)] # vector scan
<br> DT[CJ(unique(Species), c(1.5, 2.0)), nomatch=0L]
<br>
<br>
<br>Thanks,
<br>Garrett
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