Dear all,
I am facing a challenge when applying the outer product with a matrix by rows.
What I have is a rather big matrix, which I would like to convert into a
different matrix by doing something like
outer(matrix_row, vector, function(x,y) x[1]+5*x[4]/y)
In order to get there, I tried to get the matrix into a list using the mefa
package, as subsetting the original data appears too complicated. However, if I
apply the following code I always get a dimensional error, as the unlist()
function is applied to the whole list.
library(mefa)
a<-matrix(c(1:6),ncol=3)
b<-c(1,2,3,4)
a<-mat2list(a,MARGIN=1)
outer(a,b,function(x,y){unlist(a)[1]+unlist(a)[3]/b})
Any idea how to do this more elegantly than a nested for-loop?
Many thanks,
Ingo
[[alternative HTML version deleted]]
On Aug 7, 2012, at 9:02 PM, Ingo Reinhold wrote:> Dear all, > > I am facing a challenge when applying the outer product with a > matrix by rows. > > What I have is a rather big matrix, which I would like to convert > into a different matrix by doing something like > > outer(matrix_row, vector, function(x,y) x[1]+5*x[4]/y)> > In order to get there, I tried to get the matrix into a list using > the mefa package, as subsetting the original data appears too > complicated. However, if I apply the following code I always get a > dimensional error, as the unlist() function is applied to the whole > list. > > library(mefa) > a<-matrix(c(1:6),ncol=3) > b<-c(1,2,3,4) > a<-mat2list(a,MARGIN=1) > > outer(a,b,function(x,y){unlist(a)[1]+unlist(a)[3]/b})(You really should not be referring to a and b inside that function body. It's arguments are now named x and y.) Can you tell us what the answer _should_ be for the first entry? And a step by step illustration of how you got there? If this is not what it should be, then you need to read up on the expected result of the division of a scalar by a vector in R. apply(a, 1, function(x) { x[1] + x[3]/ b } ) [,1] [,2] [1,] 6.000000 8.0 [2,] 3.500000 5.0 [3,] 2.666667 4.0 [4,] 2.250000 3.5> > > Any idea how to do thisDo "this" is still somewhat nebulous.> more elegantly than a nested for-loop? > > Many thanks, > > Ingo >David Winsemius, MD Alameda, CA, USA
Can you post what you want your answer to be for the a and b you have given
already?
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Ingo Reinhold <ingor at kth.se> wrote:
>Dear all,
>
>I am facing a challenge when applying the outer product with a matrix
>by rows.
>
>What I have is a rather big matrix, which I would like to convert into
>a different matrix by doing something like
>
>outer(matrix_row, vector, function(x,y) x[1]+5*x[4]/y)
>
>In order to get there, I tried to get the matrix into a list using the
>mefa package, as subsetting the original data appears too complicated.
>However, if I apply the following code I always get a dimensional
>error, as the unlist() function is applied to the whole list.
>
>library(mefa)
>a<-matrix(c(1:6),ncol=3)
>b<-c(1,2,3,4)
>a<-mat2list(a,MARGIN=1)
>
>outer(a,b,function(x,y){unlist(a)[1]+unlist(a)[3]/b})
>
>
>Any idea how to do this more elegantly than a nested for-loop?
>
>Many thanks,
>
>Ingo
>
> [[alternative HTML version deleted]]
>
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