Extracts one cell per row (column) from a matrix
Extracts one cell per row (column) from a matrix. The implementation is optimized for memory and speed.
rowCollapse(x, idxs, rows = NULL, dim. = dim(x), ...) colCollapse(x, idxs, cols = NULL, dim. = dim(x), ...)
x |
An NxK |
idxs |
An index |
rows, cols |
A |
dim. |
An |
... |
Not used. |
Returns a vector of length N (K).
Henrik Bengtsson
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)
y_truth <- 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, y_truth))Please choose more modern alternatives, such as Google Chrome or Mozilla Firefox.