On Nov 19, 2011, at 9:32 AM, R. Michael Weylandt wrote:
Here's one approach:
A=matrix(1:15,5)
B=matrix(15:29,5)
C=matrix(30:44,5)
do.call(cbind, lapply(c("A","B","C"),function(x) get(x)[c(1,5),1]))
Also:
sapply( list(A,B,C), function(x) do.call("[", list(x, c(1,5))) )
Notice that this actually was extracting using what might be called
the "vector positions". If you wanted to use the i,j version of "["
then you would need an extra column (this example pulling the second
columns in the rows selected:
> sapply(list(A,B,C),function(x) do.call("[", list(x, c(1,5), 2)) )
[,1] [,2] [,3]
[1,] 6 20 35
[2,] 10 24 39
Comments on the differences: Michaels version used cbind to get the
ruslt in a matrix, whereas mine used sapply. His used the get function
to extract the objects from a character vector, whereas mine never
constructed a character vector. Which one you deploy will depend on
your data setup. If you already have these in a list, mine might be
easier, but if they constitute an easily constructed set of names you
might use LETTERS[] numbers and paste() to build your list of object
names.
--
david.
Michael
On Thu, Nov 17, 2011 at 9:44 PM, .Jpg <jporob...@gmail.com> wrote:
Hi everyone, I tried to solve this problem but I could not find the
solution. I have about 105 matrices of equal size in the memory
of**R, I
need to do is extract from these matrices some known positions and
create a new matrix with these columns. Show you an example with only
three matrices (but in my case I have hundreds of them).
A=matrix(1:15,5)
[,1] [,2] [,3]
[1,] 1 6 11
[2,] 2 7 12
[3,] 3 8 13
[4,] 4 9 14
[5,] 5 10 15
B=matrix(15:29,5)
[,1] [,2] [,3]
[1,] 15 20 25
[2,] 16 21 26
[3,] 17 22 27
[4,] 18 23 28
[5,] 19 24 29
C=matrix(30:44,5)
[,1] [,2] [,3]
[1,] 30 35 40
[2,] 31 36 41
[3,] 32 37 42
[4,] 33 38 43
[5,] 34 39 44
The positions I wish to extract are 1 and 5 of the first row of each
matrix (in my case are 25positions) and with this generate a new
matrix
with the form
d=
[,1] [,2] [,3]
[1,] 1 15 30
[2,] 5 19 34
The ideais to builda loop toextract thisinformation from
hundredsmatrices, butI failed todo so.
Any helpwould be greatthank you very muchin advance
regards
.jpg
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David Winsemius, MD
West Hartford, CT
______________________________________________
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