# [R] Using apply with more than one matrix

Waichler, Scott R Scott.Waichler at pnnl.gov
Wed Apr 30 22:21:50 CEST 2014

```Ok, here is a toy example.  I want to use a custom function that depends on more than one matrix/array as input, and I can't figure out how to do that with apply.

v <- c(NA, 1.5, NA, NA,
NA, 1.1, 0.5, NA,
NA, 1.3, 0.4, 0.9)
a1 <- array(v, dim=c(2,2,3))
m1 <- matrix(c(NA, 1.5, 2.1, NA), ncol=2, byrow=T)
m2 <- matrix(runif(n=4, min=1, max=3), ncol=2)
condition1 <- ifelse(!is.na(m1) & m1 > m2, T, F)

ans <- matrix(NA, ncol=2, nrow=2) # initialize
for(i in 1:2) {
for(j in 1:2) {
ind.not.na <- which(!is.na(a1[i,j,]))
if(condition1[i,j] && length(ind.not.na) > 0) {
ans[i,j] <- a1[i,j,ind.not.na] + m2[i,j]
}
}
}

Scott Waichler

> -----Original Message-----
> From: Bert Gunter [mailto:gunter.berton at gene.com]
> Sent: Wednesday, April 30, 2014 12:18 PM
> To: Waichler, Scott R
> Cc: r-help at r-project.org
> Subject: Re: [R] Using apply with more than one matrix
>
> Scott:
>
> Your problem specification is rather vague: What do you mean by "use"?
>
> In general, matrices are merely vectors with a dim attribute, so if you
> can do what you want with them as vectors, then that will work for them as
> matrices. For example:
>
> > m1<- matrix(1:6, nr=3)
> > m2 <- matrix(11:16, nr=2)
> > m2*m2
>      [,1] [,2] [,3]
> [1,]  121  169  225
> [2,]  144  196  256
>
> If this does not meet your needs, you will have to follow the posting
> guide and provide both code and a minimal reproducible example.
>
> Cheers,
> Bert
>
>
> Bert Gunter
> Genentech Nonclinical Biostatistics
> (650) 467-7374
>
> "Data is not information. Information is not knowledge. And knowledge is
> certainly not wisdom."
> H. Gilbert Welch
>
>
>
>
> On Wed, Apr 30, 2014 at 10:54 AM, Waichler, Scott R
> <Scott.Waichler at pnnl.gov> wrote:
> > Hi,
> >
> > I want to apply a custom function to all the elements of one matrix.
> The function uses the value in the same i,j in a second matrix.  How can I
> use apply() or similar function to avoid nested loops in i and j?
> >
> > Thanks,
> > Scott Waichler
> > Pacific Northwest National Laboratory
> > Richland, WA, USA
> >
> > ______________________________________________
> > R-help at r-project.org mailing list
> > https://stat.ethz.ch/mailman/listinfo/r-help