Everyone,
The |varA...varZ| construct is borrowed from STATA syntax. Probably a
reason why it got into subset() in the first place, though definitely
not very R-like. In fact I’ve never come across this construct in R
before and had no idea it was actually working either!
I’m not sure |dt[, .SD, .SDcols=list(varA...varZ)]| is less typing, less
prone to error, or more readable than |dt[, .SD,
.SDcols=names(dt)[1:24]| and using indices is also more flexible (what
about if we want more complex sequences). I can see one use case for
this syntax though if |dt| might change over time but variables always
come in known sequences.
Not sure we should really encourage it — but agreed with Arun, if it’s
in base::subset() then no reason why not.
—Mel.
On 2/10/2015 1:50 PM, Arunkumar Srinivasan wrote:
I had the same reaction when I found out ‘subset’ already did this :-).
I’ve the same impression that it’s a bit odd, even though some
people prefer it..
Arun
On 10 Feb 2015 at 19:39:29, Chris Neff ([email protected]) wrote:
Wow, didn’t realize that worked! So there is precedent then. It
just looks funny to me, but you are right it is easily avoided.
I just didn’t want to see more divergence from subset and
data.frame logic, but since this already works with subset
that’s fine.
On Tue Feb 10 2015 at 1:34:03 PM Arunkumar Srinivasan
[email protected] <http://mailto:[email protected]> wrote:
|Chris,
But what’s the problem? You can simply not use it?
It’s not that uncommon. `base::subset()` does this.
--
Arun
On 10 Feb 2015 at 19:31:43, Chris Neff ([email protected]) wrote:
|
|I don't like this idea. It adds extra that it doesn't need to.
Doing it with column numbers is more straightforward, and if all you have is
names you can get numbers by doing match() or whatever and then getting the
sequence with seq(). Having a sequence of column names is odd.
On Tue Feb 10 2015 at 1:28:25 PM Arunkumar Srinivasan
<[email protected]> wrote:
Farrel,
It could be useful. Please file an issue on the github project
page. Thanks.
--
Arun
On 10 Feb 2015 at 01:08:46, Farrel Buchinsky ([email protected])
wrote:
|
| So lets say one has a data.table with the following columns
first.name, last.name, height, weight, shoe.size,
eye.color, hair.length, appendage.size, ear.length
If one wanted to just include weight through hair.length
one would have to go something such as this
dt[,list(weight, shoe.size, eye.color, hair.length)]
Is there a way to do something along the lines of
dt[,list(weight...hair.length)]
If so, can you direct me to the documentation? If not can
you build it? Is it difficult? Some data.tables have many columns.
Thanking you in anticipation.
Farrel
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Melanie BACOU
International Food Policy Research Institute
Snr. Program Manager, HarvestChoice
Work +1(202)862-5699
E-mail [email protected]
Visit www.harvestchoice.org
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