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

In matrixStats: Functions that Apply to Rows and Columns of Matrices (and to Vectors)

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), ..., useNames = TRUE)

colCollapse(x, idxs, cols = NULL, dim. = dim(x), ..., useNames = TRUE)

Arguments

x	An NxK matrix or, if dim. is specified, an N * K vector.
idxs	An index vector of (maximum) length N (K) specifying the columns (rows) to be extracted.
rows	A vector indicating subset of rows 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. Comment: The reason for this argument being named with a period at the end is purely technical (we get a run-time error if we try to name it dim).
...	Not used.
useNames	If TRUE (default), names attributes of the result are set, otherwise not.
cols	A vector indicating subset of columns to operate over. If NULL, no subsetting is done.

Value

Returns a vector of length N (K).

Author(s)

Henrik Bengtsson

See Also

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

Examples

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))

matrixStats documentation built on Sept. 11, 2024, 5:24 p.m.