matrixStats (version 0.53.0)

rowCollapse: Extracts one cell per row (column) from a matrix

Description

Extracts one cell per row (column) from a matrix. The implementation is optimized for memory and speed.

Usage

rowCollapse(x, idxs, rows = NULL, dim. = dim(x), ...)
colCollapse(x, idxs, cols = NULL, dim. = dim(x), ...)

Arguments

x

An NxK matrix.

idxs

An index vector of (maximum) length N (K) specifying the columns (rows) to be extracted.

rows, cols

A vector indicating subset of rows (and/or columns) to operate over. If NULL, no subsetting is done.

dim.

An integer vector of length two specifying the dimension of x, also when not a matrix.

...

Not used.

Value

Returns a vector of length N (K).

See Also

Matrix indexing to index elements in matrices and arrays, cf. [().

Examples

# NOT RUN {
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))
# }