[datatable-help] variable column names

[Matthew Dowle]

where ... is eval(myid)
iigc
> Or:
> DT[,lapply(.SD,sum),by=...,.SDcols=myvars]
>
>> with = FALSE will let you use literal column names
>>
>>
>> On Wed, Apr 24, 2013 at 3:29 PM, Sam Steingold <sds at gnu.org> wrote:
>>
>>> What do I do if I want to operate on several columns?
>>> E.g.,
>>> --8<---------------cut here---------------start------------->8---
>>> length(names(dt)) = 25
>>> myvars = c("col1","col4","col7")
>>> myid = "user"
>>> setkeyv(dt,myid)
>>> --8<---------------cut here---------------end--------------->8---
>>> and I want to summarize columns in myvars by myid.
>>> the point is that nowhere in the code the literal "col4" or "user" may
>>> appear.
>>>
>>> Thanks.
>>>
>>> --
>>> Sam Steingold (http://sds.podval.org/) on Ubuntu 12.10 (quantal) X
>>> 11.0.11300000
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>>> The difference between genius and stupidity is that genius has its
>>> limits.
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