[datatable-help] using J() to select for a value that is in something other than the first key

[Matthew Dowle]

I find Nabble is better for searching the archive. It seems to be
optimised for discussion list search.  Link on homepage, 'secondary' into
search box, and e.g. thread " Select from second key but not first".

> Dear Matthew
>
> Thank you for trying to guide me. Unfortunately I was not able to really
> comprehend what I was reading
>
> I entered the following into google search "site:
> lists.r-forge.r-project.org/pipermail/datatable-help/ secondary"
>
> I got many hits and I could see a discussion but could not fathom how it
> related to my question.
>
>
> Would love some help from you or someone else. I want to be able to select
> by a criterion in the second key and accept all possible values in the
> first key.
> Farrel Buchinsky
> Google Voice Tel: (412) 567-7870
>
>
>
> On Wed, Jan 18, 2012 at 22:40, Matthew Dowle <mdowle at mdowle.plus.com>
> wrote:
>
>> Hi. Try searching datatable-help for 'secondary'.
>>
>> > In setkey it is possible to have multiple columns be a key. There is
>> > however an order to it. To select all the rows by a particular value
>> in
>> > the
>> > first key is easy
>> > DT[J("a value from the first key")]
>> >
>> > It is even quite easy to select by an AND criteria that incorporates
>> the
>> > second key
>> > DT[J("a value from the first key","a value from the second key")]
>> >
>> > But what happens if one wanted to select by only one criteria being a
>> a
>> > value that must be present in the second key? I was hoping to get
>> lucky
>> by
>> > just leaving it blank. But it did not see to work.
>> >
>> > DT[J(,"a value from the second key")]
>> >
>> > I would love to know what you do.
>> >
>> >
>> > Farrel
>> > _______________________________________________
>> > 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
>>
>>
>>
>>
>>
>