Return dimension index from array with n-dimensions

a <- array(100:1,dim=c(5,4,5))
which(a == 7)

which(a == 7, arr.ind=TRUE)

Hi,

I have been dealing with some problems finding a fast way of getting to
know in what dimension a specific value is located out of an array (like
the 'which' function for a vector returns its position).
Unable to find anything about this on the internet I wrote a function
myself.

Could you please comment if such a function already exists, and if not,
please feel free to comment the function I wrote.
Hopefully resulting in the integration of such a function in a
R-packages.

Kind regards,

Niels Hintzen

#Example:

a <- array(100:1,dim=c(5,4,5))
which(a == 7)
nindex(a,7)

nindex<-function(array.,index.){
             dims <- dim(array.)
             ldim <- length(dim(array.))

             dimmy  <- matrix(NA,ncol=length(index.),nrow=ldim)
             remain <- matrix(NA,ncol=length(index.),nrow=ldim)
             remain[1,] <- index.
             for(i in 1:(length(dims)-1)){
               dimmy[i,]    <-
ceiling(remain[i,]/(prod(dims[1:(ldim-i)])))
               dimmy[i,dimmy[i,]==0] <- rev(dims)[i]
               remain[i+1,] <- index.%%prod(dims[1:(ldim-i)])
             }
             remain[length(remain[,1]),remain[length(remain[,1]),]==0]
<- dims[1]
             dimmy[1+(length(dims)-1),] <- remain[length(remain[,1]),]
             dimmy <- dimmy[dim(dimmy)[1]:1,]

return(matrix(t(dimmy),nrow=length(index.),dimnames=list(seq(1,length(in
dex.),1),dimensions=paste("dim",as.character(c(1:length(dims))),sep=""))
))}


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