Arun,
I see, I hadn’t checked base::subset() documentation carefully, but I
see it clearly now:
|subset(airquality, Temp > 80, select = c(Ozone, Temp))
subset(airquality, Day == 1, select = -Temp)
subset(airquality, select = Ozone:Wind)
|
|:| is less ambiguous than STATA’s |…| for sure. Yes, would be nice to
replicate in data.table.
—Mel.
On 2/10/2015 4:59 PM, Eduard Antonyan wrote:
Not having to type |DT| twice would increase readability/reduce
errors, especially that real-life data.tables have much longer
names. There was a related FR to this which suggested incorporating
regex and wildcard syntax - not sure what happened to it.
On Tue, Feb 10, 2015 at 3:45 PM, Arunkumar Srinivasan
[email protected] <http://mailto:[email protected]> wrote:
|Mel,
The usage would be something like:
DT[, from:to, with=FALSE]
# or
DT[, .SD, .SDcols = from:to]
where from and to are the start and end column names. I agree there’s no
real advantage in terms of typing/prone to errors.
There might be some merit in readability, as people normally remember column
names and not numbers… And this allows you to refer to the names directly
without having to type DT and then look up the column or use a match() to find
out the column programatically or do:
DT[, .SD, .SDcols = names(DT)[some_idx]]
--
Arun
On 10 Feb 2015 at 22:39:14, Bacou, Melanie ([email protected]) wrote:
|
>
|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] 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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