matrixStats (version 0.12.2)

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

## S3 method for class 'matrix':
rowCollapse(x, idxs, dim.=dim(x), ...)
  ## S3 method for class 'matrix':
colCollapse(x, idxs, dim.=dim(x), ...)

Arguments

x

An NxK matrix.

idxs

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

dim.

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

...

Not used.

Value

• Returns a vector of length N (K).

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)
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))