Hi
On 5 Jan 2006 at 15:11, Chia, Yen Lin wrote:
Date sent: Thu, 5 Jan 2006 15:11:18 -0800
From: "Chia, Yen Lin" <yen.lin.chia at intel.com>
To: <r-help at stat.math.ethz.ch>
Subject: [R] convert matrix to data frame
> Hi all,
>
>
>
> Suppose I have a 4 x 2 matrix A and I want to select the values in
> second column such that the value in first column equals to k.
>
>
>
> I gave the colnames as alpha beta, so I was trying to access the info
> using
>
>
>
> A$beta[A[,1]==k], however, I was told it's not a data frame, I can get
> the object by using dollar sign. I tried data.frame(A), but it didn't
> work.
I believe its because matrix has a bit different structure from
data.frame so its columns can not be simply called by names. But I
wonder why data.frame(A) does not work for you? See below.
> str(A)
`data.frame': 4 obs. of 2 variables:
$ alpha: num -1.181 -0.415 2.087 1.422
$ beta : num -0.0889 0.6828 -0.7035 -0.3351
> str(mat)
num [1:4, 1:2] -1.1813 -0.4152 2.0865 1.4216 -0.0889 ...
- attr(*, "dimnames")=List of 2
..$ : chr [1:4] "1" "2" "3" "4"
..$ : chr [1:2] "alpha" "beta"
> B<-data.frame(mat)
> str(B)
`data.frame': 4 obs. of 2 variables:
$ alpha: num -1.181 -0.415 2.087 1.422
$ beta : num -0.0889 0.6828 -0.7035 -0.3351
> mat$alpha[mat[,1]<0]
NULL
> B$alpha[mat[,1]<0]
[1] -1.181258 -0.415175
>
>
>
> Any input on this will be very appreciated. Thanks.
>
>
>
> I tried looking in the manual, but I think I'm might be wrong about
> the keywords.
>
>
>
> Yen Lin
>
>
> [[alternative HTML version deleted]]
>
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Petr Pikal
petr.pikal at precheza.cz