matrixStats (version 1.0.0)

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

Value

Returns a vector of length N (K).

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 FALSE (default), no naming support is done. Else if TRUE, names attributes of result are set.

cols

A vector indicating subset of columns to operate over. If NULL, no subsetting is done.

Author

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))