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

In matrixStats: Methods that apply to rows and columns of 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, ...)
  ## S3 method for class 'matrix'
colCollapse(x, idxs, ...)

Arguments

x	An NxK matrix.
idxs	An index vector of (maximum) length N (K) specifying the columns (rows) to be extracted.
...	Not used.

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)
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))

matrixStats documentation built on May 2, 2019, 4:52 p.m.