# [R] Stop R from changing matrix to numeric

Peter Alspach Peter.Alspach at plantandfood.co.nz
Wed Dec 17 19:59:34 CET 2014

```Tena koe Sachin

The following might help you understand what is going on and how to rectify it.

cost <- function(x) {x[,1]*x[,2]}
ttMat <- matrix(1:4, ncol=2)
ttMat
cost(ttMat)
cost(ttMat[1,])
cost(as.matrix(ttMat[1,]))
cost(t(as.matrix(ttMat[1,])))
cost(matrix(ttMat[1,], ncol=2))

str(ttMat)
str(ttMat[1,])
str(as.matrix(ttMat[1,]))
str(t(as.matrix(ttMat[1,])))
str(matrix(ttMat[1,], ncol=2))

HTH .....

Peter Alspach

-----Original Message-----
From: R-help [mailto:r-help-bounces at r-project.org] On Behalf Of Sachinthaka Abeywardana
Sent: Wednesday, 17 December 2014 7:55 p.m.
To: r-help at r-project.org
Subject: [R] Stop R from changing matrix to numeric

I have the following cost function:
cost<-function(x){
x[,1]*sin(4*x[,1])+1.1*x[,2]*sin(2*x[,2])
}

If I send in a matrix which has MORE than one row and 2 columns, this works fine. However, if I try to do cost(t(as.matrix(c(1,1)))) it gives me an index error. When I tried debugging it, I found that the type of matrix 'x' was converted to numeric.

How do I prevent this conversion from matrix to numeric if its a matrix with just one row? The only way it would work is if I have:
x*sin(4*x)+1.1*x*sin(2*x), which in turn wont work with a matrix input.

Thanks,
Sachin

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