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.
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x |
A |
cols |
The columns of |
na.last |
for controlling the treatment of |
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 |
allow.duplicates |
ff |
... |
optional parameters to pass to |
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.
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.
Michael J. Kane <bigmemoryauthors@gmail.com>
order
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