[datatable-help] Force evaluation of first argument to [
Bacou, Melanie
mel at mbacou.com
Fri Feb 14 13:59:05 CET 2014
Arun, thanks for the clarification -- I see I didn't read that thread fully.
--Mel.
On 2/14/2014 7:07 AM, Arunkumar Srinivasan wrote:
> Melanie,
> `set` modifies by reference. Yours'll make a copy.
> Arun
> ------------------------------------------------------------------------
> From: Bacou, Melanie Bacou, Melanie <mailto:mel at mbacou.com>
> Reply: Bacou, Melanie mel at mbacou.com <mailto:mel at mbacou.com>
> Date: February 14, 2014 at 12:52:56 PM
> To: Matt Dowle mdowle at mdowle.plus.com <mailto:mdowle at mdowle.plus.com>,
> John Laing john.laing at gmail.com <mailto:john.laing at gmail.com>
> Subject: Re: [datatable-help] Force evaluation of first argument to [
>> Hi John, Matt,
>>
>> In this case, why not simply using the standard data.table approach
>> with .SD?
>>
>> fbq.cp[, lapply(.SD, function(x) ifelse(is.na(x), FALSE, x)),
>> .SDcols=c("foo", "bar", "qux")]
>>
>> --Mel.
>>
>>
>> On 2/12/2014 2:22 PM, Matt Dowle wrote:
>>>
>>> Ha. Yes we certainly don't hold back from making the messages as
>>> long and as helpful as possible. If the code knows, or can know
>>> what exactly is wrong, it's a deliberate policy to put that info
>>> right there into the message. data.table is written by users; i.e.
>>> we wrote it for ourselves doing real jobs. I think that may be the
>>> root of that. If any messages could more helpful, those suggestions
>>> are very welcome.
>>>
>>> Matt
>>>
>>> On 12/02/14 17:58, John Laing wrote:
>>>> Thanks, Matt! With a slight amendment that works great:
>>>> for (x in c("foo", "bar", "qux")) set(fbq, which(is.na
>>>> <http://is.na>(fbq[[x]])), x, FALSE)
>>>>
>>>> Which highlights an opportunity to say that I really appreciate the
>>>> unusually helpful error messages in this package.
>>>>
>>>> -John
>>>>
>>>>
>>>> On Wed, Feb 12, 2014 at 12:44 PM, Matt Dowle
>>>> <mdowle at mdowle.plus.com <mailto:mdowle at mdowle.plus.com>> wrote:
>>>>
>>>>
>>>> Hi John,
>>>>
>>>> In examples like this I'd use set() and [[, since it's a bit
>>>> easier to write but memory efficient too.
>>>>
>>>> for (x in c("foo", "bar", "qux")) set(fbq, is.na
>>>> <http://is.na>(fbq[[x]]), x, FALSE) [untested]
>>>>
>>>> A downside here is one repetition of the "fbq" symbol, but can
>>>> live with that. If you have a large number of columns (and
>>>> I've been surprised just how many columns some poeple have!)
>>>> then calling set() many times has lower overhead than DT[,
>>>> :=], see ?set. Note also that [[ is base R, doesn't copy the
>>>> column and often useful to use with data.table.
>>>>
>>>> Or, use get() in either i or j rather than eval().
>>>>
>>>> HTH, Matt
>>>>
>>>>
>>>>
>>>> On 12/02/14 17:24, John Laing wrote:
>>>>> Let's say I merge together several data.tables such that I wind up
>>>>> with lots of NAs:
>>>>>
>>>>> require(data.table)
>>>>> foo <- data.table(k=1:4, foo=TRUE, key="k")
>>>>> bar <- data.table(k=3:6, bar=TRUE, key="k")
>>>>> qux <- data.table(k=5:8, qux=TRUE, key="k")
>>>>> fbq <- merge(merge(foo, bar, all=TRUE), qux, all=TRUE)
>>>>> print(fbq)
>>>>> # k foo bar qux
>>>>> # 1: 1 TRUE NA NA
>>>>> # 2: 2 TRUE NA NA
>>>>> # 3: 3 TRUE TRUE NA
>>>>> # 4: 4 TRUE TRUE NA
>>>>> # 5: 5 NA TRUE TRUE
>>>>> # 6: 6 NA TRUE TRUE
>>>>> # 7: 7 NA NA TRUE
>>>>> # 8: 8 NA NA TRUE
>>>>>
>>>>> I want to go through those columns and turn each NA into
>>>>> FALSE. I can
>>>>> do this by writing code for each column:
>>>>>
>>>>> fbq.cp <- copy(fbq)
>>>>> fbq.cp[is.na <http://is.na>(foo), foo:=FALSE]
>>>>> fbq.cp[is.na <http://is.na>(bar), bar:=FALSE]
>>>>> fbq.cp[is.na <http://is.na>(qux), qux:=FALSE]
>>>>> print(fbq.cp)
>>>>> # k foo bar qux
>>>>> # 1: 1 TRUE FALSE FALSE
>>>>> # 2: 2 TRUE FALSE FALSE
>>>>> # 3: 3 TRUE TRUE FALSE
>>>>> # 4: 4 TRUE TRUE FALSE
>>>>> # 5: 5 FALSE TRUE TRUE
>>>>> # 6: 6 FALSE TRUE TRUE
>>>>> # 7: 7 FALSE FALSE TRUE
>>>>> # 8: 8 FALSE FALSE TRUE
>>>>>
>>>>> But I can't figure out how to do it in a loop. More precisely,
>>>>> I can't
>>>>> figure out how to make the [ operator evaluate its first
>>>>> argument in
>>>>> the context of the data.table. All of these have no effect:
>>>>> for (x in c("foo", "bar", "qux")) fbq[is.na <http://is.na>(x),
>>>>> eval(x):=FALSE]
>>>>> for (x in c("foo", "bar", "qux")) fbq[is.na
>>>>> <http://is.na>(eval(x)), eval(x):=FALSE]
>>>>> for (x in c("foo", "bar", "qux")) fbq[eval(is.na
>>>>> <http://is.na>(x)), eval(x):=FALSE]
>>>>>
>>>>> I'm running R 3.0.2 on Linux, data.table 1.8.10.
>>>>>
>>>>> Thanks in advance,
>>>>> John
>>>>>
>>>>>
>>>>> _______________________________________________
>>>>> datatable-help mailing list
>>>>> datatable-help at lists.r-forge.r-project.org <mailto:datatable-help at lists.r-forge.r-project.org>
>>>>> https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/datatable-help
>>>>
>>>>
>>>
>>>
>>>
>>> _______________________________________________
>>> datatable-help mailing list
>>> datatable-help at lists.r-forge.r-project.org
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>>
>> --
>> Melanie BACOU
>> International Food Policy Research Institute
>> Agricultural Economist, HarvestChoice
>> Work +1(202)862-5699
>> E-mailmel at mbacou.com
>> Visit harvestchoice.org
>> _______________________________________________
>> datatable-help mailing list
>> datatable-help at lists.r-forge.r-project.org
>> https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/datatable-help
--
Melanie BACOU
International Food Policy Research Institute
Agricultural Economist, HarvestChoice
Work +1(202)862-5699
E-mail mel at mbacou.com
Visit harvestchoice.org
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