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,]Â 1Â 1
[2,]Â 2Â 1
[3,]Â 1Â 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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