rowCollapse {matrixStats} | R Documentation |
Extracts one cell per row (column) from a matrix. The implementation is optimized for memory and speed.
rowCollapse(x, idxs, ...) colCollapse(x, idxs, ...)
x |
An NxK matrix . |
idxs |
An index vector of (maximum) length N (K) specifying the
columns (rows) to be extracted. |
... |
Not used. |
Returns a vector
of length N (K).
Henrik Bengtsson (http://www.braju.com/R/)
Matrix indexing to index elements in matrices and arrays,
cf. [
().
x <- matrix(1:27, ncol=3) y <- rowCollapse(x, 1) stopifnot(identical(y, x[,1])) y <- rowCollapse(x, 2) stopifnot(identical(y, x[,2])) y <- rowCollapse(x, c(1,1,1,1,1,3,3,3,3)) stopifnot(identical(y, c(x[1:5,1], x[6:9,3]))) y <- rowCollapse(x, 1:3) print(y) yT <- c(x[1,1],x[2,2],x[3,3],x[4,1],x[5,2],x[6,3],x[7,1],x[8,2],x[9,3]) stopifnot(identical(y, yT))