[R] Matrix of indexes to extract sparse data in dataframe

[Sergio Fonda]

Thank you very much!
Il 05/giu/2015 15:58, "David L Carlson" <dcarlson at tamu.edu> ha scritto:

> You can select elements of a matrix using a 2 dimensional matrix that
> specifies the row/column number of the cells you want to extract:
>
> > c2 <- cbind(seq_len(nrow(c0)), c1)
> > c2
>        c1
> [1,] 1  2
> [2,] 2  2
> [3,] 3  1
> [4,] 4  2
> [5,] 5  1
> [6,] 6  1
> > d1 <- c0[c2]
> > d1
> [1]  -1  -3  12   2 -23  17
>
> See the help page for [
>
> ?'['
>
> -------------------------------------
> David L Carlson
> Department of Anthropology
> Texas A&M University
> College Station, TX 77840-4352
>
>
> -----Original Message-----
> From: R-help [mailto:r-help-bounces at r-project.org] On Behalf Of Sergio
> Fonda
> Sent: Friday, June 5, 2015 8:47 AM
> To: John Kane
> Cc: R-help
> Subject: Re: [R] Matrix of indexes to extract sparse data in dataframe
>
> Thank you, of course but I can't use that form as I told. My question is
> about the possibility to enter in a dataframe with a matrix of indices and
> get the corresponding values
> Thanks again
>  Il 05/giu/2015 15:39, "John Kane" <jrkrideau at inbox.com> ha scritto:
>
> > d1  <-  apply(c0, 1, min)  I think does it.
> >
> > John Kane
> > Kingston ON Canada
> >
> >
> > > -----Original Message-----
> > > From: sergio.fonda99 at gmail.com
> > > Sent: Fri, 5 Jun 2015 15:06:34 +0200
> > > To: r-help at r-project.org
> > > Subject: [R] Matrix of indexes to extract sparse data in dataframe
> > >
> > > I would like to avoid a "for loop" to get a vector of data taken from
> > > rows of a data frame for specific columns.
> > > An example is the following (I can't apply min to every row of df, this
> > > is
> > > just an example):
> > >
> > > c0=data.frame(a=c(3,-2,12,7,-23,17) , b=c(-1,-3,14,2,6,19))
> > > c1=apply(c0,1,which.min)
> > >> c1
> > > [1] 2 2 1 2 1 1
> > >
> > > I would like to get a result like the following call, but without
> > > employing a "for loop":
> > >
> > > d1=c(c0[1,c1[1]], c0[2,c1[2]], c0[3,c1[3]], c0[4,c1[4]], c0[5,c1[5]],
> > > c0[6,c1[6]])
> > >> d1
> > > [1]  -1  -3  12   2 -23  17
> > >
> > > Thanks a lot for any help!
> > >
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> ______________________________________________
> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
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