As Peter and Bart I really have a problem understanding you.
Perhaps if you tell us what your desired result is going to used for we can be
more helpful. You can do that using your latest example.
In that example you want a matrix of sets of row and column indices. This will
probably have to be a matrix of characters. There you go from a 3Ã4 matrix to
a 3Ã2 matrix. What do you want in case of Barts 2Ã2 matrix? A 3Ã1 or 1Ã3
matrix? And in a more general case?
Best regards
Frede
Sendt fra Samsung mobil
-------- Oprindelig meddelelse --------
Fra: carol white
Dato:19/06/2014 15.18 (GMT+01:00)
Til: Bart Kastermans
Cc: r-help@r-project.org
Emne: Re: [R] extract a subset of non-contiguous elements of a matrix
tm.1=rbind(c(1,-3,2,-4), c(1,-3,2,-4),c(1,-3,2,-4))
> which(tm.1 > 0, arr.ind=TRUE)
row col
[1,] 1 1
[2,] 2 1
[3,] 3 1
[4,] 1 3
[5,] 2 3
[6,] 3 3
so the answer should have the elements of tm.1 with the following indexes
1,1 1,3
2,1 2,3
3,1 3,3
On Thursday, June 19, 2014 3:08 PM, Bart Kastermans <kaste...@kasterma.net>
wrote:
If you give an example of input and desired output I can think about this. But
at this
point I do not understand what you want. In the example I gave the positive
elements do
not form a submatrix in any way I can think of.
On 19 Jun 2014, at 15:04, carol white <wht_...@yahoo.com> wrote:
> well it gives a vector which is useless as I want a matrix.
>
>
> On Thursday, June 19, 2014 2:40 PM, Bart Kastermans <kaste...@kasterma.net>
> wrote:
>
>
> > tm.1 <- matrix(c(11,22,33,-4), ncol=2)
> > which(tm.1 > 0, arr.ind=TRUE)
> row col
> [1,] 1 1
> [2,] 2 1
> [3,] 1 2
> > tm.1[which(tm.1 > 0, arr.ind=TRUE)]
> [1] 11 22 33
>
> This last command does what you ask I think.
>
> On 19 Jun 2014, at 14:12, carol white <wht_...@yahoo.com> wrote:
>
> > The extracted values don't form a matrix and that's the question how to
> > extract because which returns the indexes? that is, from
> > 1,1
> > 2,1
> > 1,2
> >
> > how to retrieve values?
> >
> > Or if at the position 2,1, there is a negative value, how to retrieve
> > 1,1
> > 1,2
> >
> >
> > Carol
> >
> >
> > On Thursday, June 19, 2014 1:29 PM, Bart Kastermans <kaste...@kasterma.net>
> > wrote:
> >
> >
> > On 19 Jun 2014, at 13:19, carol white <wht_...@yahoo.com> wrote:
> >
> > > Hi,
> > > Is there a way to extract a subset of non-contiguous elements of a matrix
> > > elegantly and with 1 or very few scripts?
> > >
> > > Suppose I have a matrix of positive and negative numbers (m) and I want
> > > to retrieve only the positive number. This I can do
> > >
> > > which(m>0, arr.ind=T) which gives the indices of positive elements like
> > > (37,1), (80,1), ..., (54,2) etc. How can I extract positive numbers
> > > without looping on the indexes provided by which to make a new matrix?
> >
> > What matrix do you want? For e.g.
> >
> > > tm.1 <- matrix(c(11,22,33,-4), ncol=2)
> > > which(tm.1 > 0, arr.ind=TRUE)
> > row col
> > [1,] 1 1
> > [2,] 2 1
> > [3,] 1 2
> > > tm.1[which(tm.1 > 0, arr.ind=TRUE)]
> > [1] 11 22 33
> >
> > The extracted values do not form a matrix.
> >
> > Either the above contains the answer, or I donât understand the question.
> >
> > Best,
> > Bart
> >
> >
> > >
> > > thanks,
> > >
> > > Carol
> >
> >
>
>
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