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

[Farrel Buchinsky]

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
>
>
>
>
>
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