Ordering and row-permuting functions for “big.matrix” and “matrix” objects

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Description

The morder function returns a permutation of row indices which can be used to rearrangea 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

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morder(x, cols, na.last=TRUE, decreasing = FALSE)
mpermute(x, order=NULL, cols=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?

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 dupicated 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 specifed 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 <bigmemoryauthors@gmail.com>

See Also

order

Examples

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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]