morder: Ordering and Permuting functions for big.matrix" and matrix"...

In bigmemory: Manage Massive Matrices with Shared Memory and Memory-Mapped Files

Ordering and Permuting functions for ⁠big.matrix'' and ⁠matrix” objects

Description

The morder function returns a permutation of row indices which can be used to rearrange an object according to the values in the specified columns (a multi-column ordering). The mpermute function actually reorders the rows of a big.matrix or matrix based on an order vector or a desired ordering on a set of columns.

Usage

morder(x, cols, na.last = TRUE, decreasing = FALSE)

morderCols(x, rows, na.last = TRUE, decreasing = FALSE)

mpermute(x, order = NULL, cols = NULL, allow.duplicates = FALSE, ...)

mpermuteCols(x, order = NULL, rows = NULL, allow.duplicates = FALSE, ...)

Arguments

x	A big.matrix or matrix object with numeric values.
cols	The columns of x to get the ordering for or reorder on
na.last	for controlling the treatment of NAs. If TRUE, missing values in the data are put last; if FALSE, they are put first; if NA, they are removed.
decreasing	logical. Should the sort order be increasing or decreasing?
rows	The rows of x to get the ordering for or reorder on
order	A vector specifying the reordering of rows, i.e. the result of a call to order or morder.
allow.duplicates	ff TRUE, allows a row to be duplicated in the resulting big.matrix or matrix (i.e. in this case, order would not need to be a permutation of 1:nrow(x)).
...	optional parameters to pass to morder when cols is specified instead of just using order.

Details

The morder function behaves similar to order, returning a permutation of 1:nrow(x) which rearranges objects according to the values in the specified columns. However, morder takes a big.matrix or an R matrix (with numeric type) and a set of columns (cols) with which to determine the ordering; morder does not incur the same memory overhead required by order, and runs more quickly.

The mpermute function changes the row ordering of a big.matrix or matrix based on a vector order or an ordering based on a set of columns specified by cols. It should be noted that this function has side-effects, that is x is changed when this function is called.

Value

morder returns an ordering vector. mpermute returns nothing but does change the contents of x. This type of a side-effect is generally frowned upon in R, but we “break” the rules here to avoid memory overhead and improve performance.

Author(s)

Michael J. Kane [e-mail]

See Also

order

Examples

m = matrix(as.double(as.matrix(iris)), nrow=nrow(iris))
morder(m, 1)
order(m[,1])

m[order(m[,1]), 2]
mpermute(m, cols=1)
m[,2]

bigmemory documentation built on May 29, 2024, 12:18 p.m.