R Graphical Manual

Browse All

Last data update: 2014.03.03

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

rowCollapse

R Documentation

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).

Author(s)

Henrik Bengtsson

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))