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<blockquote type="cite"><div dir="ltr">> dt[, sum(V2), by = V1]<br> V1 V1<br>1: 1 2<br></div></blockquote><div>Eddi, the simplest explanation is, since we generate auto-names, we should check if the V-series names exist and if so, generate the next one automatically. That is, in this case, my thought process is, "V1" is the grouping column and it's going to be retained. "V2" is in "J", but it has no name. So, we should be able to decide that "V1" is already taken and assign "V2" automatically. At least, that's what I think *should* happen. We can check for the names to "list(…)" argument in "j" to do this, I think, not sure though.</div><div><br></div>
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<div><div><br></div><div>Arun</div><div><br></div></div>
<p style="color: #A0A0A8;">On Sunday, November 3, 2013 at 1:43 AM, Eduard Antonyan wrote:</p>
<blockquote type="cite" style="border-left-style:solid;border-width:1px;margin-left:0px;padding-left:10px;">
<span><div><div><div dir="ltr">Tbh I don't see why data presentation and preservation (i.e. if you're reading in data with duplicated columns) is not enough of a use case - that's the only reason we allow arbitrary symbols in column names.<br>
<br>So, instead of giving you another use case, how about you tell me instead what do you propose should happen here (instead of what happens now):<br><br>> dt = data.table(1, 2)<br>> dt<br> V1 V2<br>1: 1 2<br>
> dt[, sum(V2), by = V1]<br>
V1 V1<br>1: 1 2<br><br><br></div><div><br><br><div>On Sat, Nov 2, 2013 at 7:36 PM, Arunkumar Srinivasan <span dir="ltr"><<a href="mailto:aragorn168b@gmail.com" target="_blank">aragorn168b@gmail.com</a>></span> wrote:<br><blockquote type="cite"><div>
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Eddi,
</div><div>While loading the data in, maybe, if it is essential to keep names intact, we can probably add an argument, "asis=TRUE" or something like that. But I don't see a reason for doing anything else in `data.table` using duplicate names and trying to catch errors when nothing meaningful can be done with them. Besides data presentation, can you tell any other use with them?</div>
<div><div><br></div><div>Arun</div><div><br></div></div><div><div>
<p style="color:#a0a0a8">On Sunday, November 3, 2013 at 1:31 AM, Eduard Antonyan wrote:</p><blockquote type="cite"><div>
<span><div><div><div dir="ltr"><div><div><div>The main usage case I've personally encountered is data presentation (for either self or others), where I would sometimes organize data like so:<br><br>
</div>category1 name,colname1,colname2,category2 name,colname1,colname2<br>
</div>....numbersandstuff....<br><br></div><div>Also, in general there are many cases I brought up above that generate duplicate names, and I definitely don't want either lost columns or renamed columns as a result - both are data loss that I don't appreciate.<br>
</div></div><div><br><br><div>On Sat, Nov 2, 2013 at 7:10 PM, Steve Lianoglou <span dir="ltr"><<a href="mailto:lianoglou.steve@gene.com" target="_blank">lianoglou.steve@gene.com</a>></span> wrote:<br><blockquote type="cite"><div>
<div>Hi,<br>
<br>
On Sat, Nov 2, 2013 at 8:41 AM, Arunkumar Srinivasan<br>
<<a href="mailto:aragorn168b@gmail.com" target="_blank">aragorn168b@gmail.com</a>> wrote:<br>
[snip]<br>
<div>> Overall, I agree keeping duplicate names may help some users. But then, the<br>
> potential side-effects should be marked with warnings/errors distinctly, in<br>
> all cases (and preferably documented).<br>
</div>[/snip]<br>
<br>
I guess I must have missed it, but has anyone anywhere (in this<br>
thread, a FR or something) actually present a (concrete) compelling<br>
situation where allowing duplicate column names was actually useful?<br>
<br>
I'm hard pressed to come up with any situation where (purposefully)<br>
keeping duplicate column names in a data.table has more benefit than<br>
downside. Seems to me that if this ever happens, it most certainly<br>
would be by mistake.<br>
<br>
Can someone help me out here?<br>
<br>
In the case of cbinding two data.tables together that end up having<br>
two duplicate names, I'd imagine unique-ing the names of the<br>
data.tables and firing a warning that this was done would be most<br>
useful (uniqueness priority would be from left to right as the<br>
data.tables are passed into the cbind call)<br>
<span><font color="#888888"><br>
-steve<br>
<br>
--<br>
Steve Lianoglou<br>
Computational Biologist<br>
Bioinformatics and Computational Biology<br>
Genentech<br>
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