# combinations: Enumerate the Combinations of the Elements of a Vector In OBsMD: Objective Bayesian Model Discrimination in Follow-Up Designs

 combinations R Documentation

## Enumerate the Combinations of the Elements of a Vector

### Description

`combinations` enumerates the possible combinations of a specified size from the elements of a vector.

### Usage

``````combinations(n, r, v=1:n, set=TRUE, repeats.allowed=FALSE)
``````

### Arguments

 `n` Size of the source vector `r` Size of the target vectors `v` Source vector. Defaults to `1:n` `set` Logical flag indicating whether duplicates should be removed from the source vector `v`. Defaults to `TRUE`. `repeats.allowed` Logical flag indicating whether the constructed vectors may include duplicated values. Defaults to `FALSE`.

### Details

Caution: The number of combinations increases rapidly with `n` and `r`!.

To use values of `n` above about 45, you will need to increase R's recursion limit. See the `expression` argument to the `options` command for details on how to do this.

### Value

Returns a matrix where each row contains a vector of length `r`.

### Author(s)

Original versions by Bill Venables Bill.Venables@cmis.csiro.au. Extended to handle `repeats.allowed` by Gregory R. Warnes greg@warnes.net.

### References

Venables, Bill. "Programmers Note", R-News, Vol 1/1, Jan. 2001. https://cran.r-project.org/doc/Rnews/

### Examples

``````combinations(3,2,letters[1:3])
combinations(3,2,c(1:3),repeats=TRUE)
combinations(6,3,1:6,repeats=TRUE)

# To use large 'n', you need to change the default recusion limit
options(expressions=1e5)
cmat <- combinations(100,2)
dim(cmat) # 4950 by 2
``````

OBsMD documentation built on Nov. 14, 2023, 5:10 p.m.