# Array position to matrix coordinates conversion

May 30, 2011
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(This article was first published on me nugget, and kindly contributed to R-bloggers)

`#A function that is sometimes useful in determining the #coordinate(i.e. row and column number) of a matrix position#(and vice-versa). #Either a vector of positions ("pos") #OR a 2 column matrix of matrix coordinates, ("coord", i.e. cbind(row,col)), #AND the matrix dimentions must be supplied (dim.mat, i.e. c(nrow,ncol)).pos2coord<-function(pos=NULL, coord=NULL, dim.mat=NULL){ if(is.null(pos) & is.null(coord) | is.null(dim.mat)){  stop("must supply either 'pos' or 'coord', and 'dim.mat'") } if(is.null(pos) & !is.null(coord) & !is.null(dim.mat)){  pos <- ((coord[,2]-1)*dim.mat[1])+coord[,1]   return(pos) } if(!is.null(pos) & is.null(coord) & !is.null(dim.mat)){  coord <- matrix(NA, nrow=length(pos), ncol=2)  coord[,1] <- ((pos-1) %% dim.mat[1]) +1  coord[,2] <- ((pos-1) %/% dim.mat[1]) +1  return(coord) }}`

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