expandGridSample: Sample the Cartesian Product

In RcppAlgos: High Performance Tools for Combinatorics and Computational Mathematics

Sample the Cartesian Product

Description

• Generate a specific (lexicographically) or random sample of the Cartesian product of the input vectors.

• Produce results in parallel using the nThreads arguments.

• GMP support allows for exploration where the number of results is large.

Usage

expandGridSample(
    ..., n = NULL, sampleVec = NULL, seed = NULL,
    nThreads = NULL, namedSample = FALSE, return_df = FALSE
)

Arguments

...	vectors, factors or a list containing these. (See ?expand.grid).
n	Number of results to return. The default is NULL.
sampleVec	A vector of numbers representing the lexicographical partition of groups to return. Accepts vectors of class bigz as well as vectors of characters
seed	Random seed initialization. The default is NULL. N.B. If the gmp library is needed, this parameter must be set in order to have reproducible results (E.g set.seed() has no effect in these cases).
nThreads	Specific number of threads to be used. The default is NULL.
namedSample	Logical flag. If TRUE, rownames corresponding to the lexicographical result, will be added to the returned matrix. The default is FALSE.
return_df	Logical flag to force the output to be a data.frame. The default is FALSE.

Details

These algorithms rely on efficiently generating the n^{th} lexicographical result.

Value

When all of the input is of the same type, by default expandGridSample produces a matrix (a data.frame otherwise). This can be ignored by setting the argument return_df = TRUE.

Author(s)

Joseph Wood

References

Lexicographical order

Examples

## input vectors
lst = list(factor(state.abb), euro, islands)

## generate 10 random products
expandGridSample(lst, n = 10, seed = 123)

## using sampleVec to generate specific results
expandGridSample(lst, sampleVec = c(1, 100, 1e3))

all.equal(expandGridSample(lst, sampleVec = 1:expandGridCount(lst)),
         expandGrid(lst))

## Examples with enormous number of total results
big_lst = Map(function(x, y) x:y, 8:33, 15:40)
num = expandGridCount(big_lst)
gmp::log2.bigz(num)
## [1] 78

first = gmp::urand.bigz(n = 1, size = 78, seed = 123)
mySamp = do.call(c, lapply(0:10, function(x) gmp::add.bigz(first, x)))

class(mySamp)
## [1] "bigz"

## using the sampling function
cartSamp = expandGridSample(big_lst, sampleVec = mySamp)

## using the standard function
cartGeneral = expandGrid(big_lst,
                         lower = first,
                         upper = gmp::add.bigz(first, 10))

identical(cartSamp, cartGeneral)
## [1] TRUE

RcppAlgos documentation built on March 8, 2026, 9:08 a.m.