<div dir="ltr"><div class="gmail_extra"><div class="gmail_quote"><div class="gmail_default" style="font-family:tahoma,sans-serif;color:rgb(0,51,51)">Thanks a lot guys, I was sure that was possible</div><div class="gmail_default" style="font-family:tahoma,sans-serif;color:rgb(0,51,51)"></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex"><div class="gmail_default" style="font-family:tahoma,sans-serif;color:rgb(0,51,51);display:inline"></div><span style="font-size:12.8000001907349px">The first list is for the syntax - (cols) := list(values)</span><span style="color:rgb(0,51,51);font-family:tahoma,sans-serif"></span></blockquote><div><br></div><div><div class="gmail_default" style="font-family:tahoma,sans-serif;color:rgb(0,51,51)">Ok, I forgot this point</div><br></div><br></div><div class="gmail_quote">2015-06-25 15:53 GMT-04:00 Arunkumar Srinivasan <span dir="ltr"><<a href="mailto:aragorn168b@gmail.com" target="_blank">aragorn168b@gmail.com</a>></span>:<br><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex"><div style="word-wrap:break-word"><div style="font-family:Helvetica,Arial;font-size:13px;color:rgb(0,0,0);margin:0px">To add to Frank’s reply, I think `dt[, V3 := .(list(V1)), by=V2]` doesn’t work with `1.9.4`, but has been fixed in 1.9.5.</div>The first list is for the syntax - (cols) := list(values). Cases like `DT[, A := 1:5]` and is internally wrapped by `list()` for convenience, as they are very common use cases.<div><span class=""><font color="#888888"> <div><div style="font-family:helvetica,arial;font-size:13px">-- <br>Arun</div></div></font></span><div><div class="h5"> <br><p style="color:rgb(0,0,0)">On 25 Jun 2015 at 21:51:09, Frank Erickson (<a href="mailto:fperickson@wisc.edu" target="_blank">fperickson@wisc.edu</a>) wrote:</p> <blockquote type="cite"><span><div><div></div><div>
<div dir="ltr">Oh, sorry, didn't notice you were making a new
column, in that case: dt[,V3:=list(list(V1)),by=V2]
<div><br></div>
</div>
<div class="gmail_extra"><br>
<div class="gmail_quote">On Thu, Jun 25, 2015 at 3:48 PM, Frank
Erickson <span dir="ltr"><<a href="mailto:fperickson@wisc.edu" target="_blank">fperickson@wisc.edu</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex">
<div dir="ltr">Hi,
<div><br></div>
<div>I think you want</div>
<div><br></div>
<div><font face="monospace, monospace">dt[,.(list(V1)),by=V2]<br></font></div>
<div>
<div><font face="monospace, monospace"># V2
V1</font></div>
<div><font face="monospace, monospace"># 1: a
1,4</font></div>
<div><font face="monospace, monospace"># 2: b
2,3</font></div>
</div>
<div><br></div>
<div><br></div>
<div>Using the .() notation makes it easier to keep track of what
columns are being made, I find.</div>
<div><br></div>
<div>--Frank</div>
</div>
<div class="gmail_extra"><br>
<div class="gmail_quote">
<div>
<div>On Thu, Jun 25, 2015 at 3:46 PM, Nicolas Paris
<span dir="ltr"><<a href="mailto:niparisco@gmail.com" target="_blank">niparisco@gmail.com</a>></span> wrote:<br></div>
</div>
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex">
<div>
<div>
<div dir="ltr">
<div style="font-family:tahoma,sans-serif;color:rgb(0,51,51)">Hi,</div>
<div style="font-family:tahoma,sans-serif;color:rgb(0,51,51)"><br></div>
<div style="font-family:tahoma,sans-serif;color:rgb(0,51,51)">Here an example
what I want to get :</div>
<div style="font-family:tahoma,sans-serif;color:rgb(0,51,51)"><br></div>
<div><font color="#003333" face="tahoma, sans-serif">> dt <-
data.table(c(1,2,3,4),c("a","b","b","a"))</font><br></div>
<div>
<div><font color="#003333" face="tahoma, sans-serif">> dt</font></div>
<div><font color="#003333" face="tahoma, sans-serif"> V1 V2</font></div>
<div><font color="#003333" face="tahoma, sans-serif">1: 1 a</font></div>
<div><font color="#003333" face="tahoma, sans-serif">2: 2 b</font></div>
<div><font color="#003333" face="tahoma, sans-serif">3: 3 b</font></div>
<div><font color="#003333" face="tahoma, sans-serif">4: 4 a</font></div>
<div><font color="#003333" face="tahoma, sans-serif"><br></font></div>
<div><font color="#003333" face="tahoma, sans-serif">What I want to get is a V3 column, containing
an aggregated vector :</font></div>
<div>
<div><font color="#003333" face="tahoma, sans-serif">> dt</font></div>
<div><font color="#003333" face="tahoma, sans-serif"> V1 V2 V3</font></div>
<div><font color="#003333" face="tahoma, sans-serif">1: 1 a c(1,4)</font></div>
<div><font color="#003333" face="tahoma, sans-serif">2: 2 b c(2,3)</font></div>
<div><font color="#003333" face="tahoma, sans-serif"><br></font></div>
<div><font color="#003333" face="tahoma, sans-serif">That does not work :</font></div>
<div><font color="#003333" face="tahoma, sans-serif"><br></font></div>
<div><font color="#003333" face="tahoma, sans-serif">dt[,V3 := as.list(c(V1)),by=V2]</font></div>
<div><font color="#003333" face="tahoma, sans-serif"><br></font></div>
<div><font color="#003333" face="tahoma, sans-serif">Is there a way to do so ?</font></div>
<div><font color="#003333" face="tahoma, sans-serif"><br></font></div>
<div><font color="#003333" face="tahoma, sans-serif">Thanks</font></div>
<div><font color="#003333" face="tahoma, sans-serif"><br></font></div>
<div><font color="#003333" face="tahoma, sans-serif"><br></font></div>
</div>
</div>
</div>
<br></div>
</div>
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