Pairwise combinations of variables that will be the result of a function applied to each combination.

## Arguments

- .data
A matrix of data with, say, p columns.

- order
The order on how the results will appear in the output. Default is

`order = 'first'`

. In this case, assuming that .data has four columns, namely,`V1, V2, V3, V4`

, the order of columns in the output will be`V1.V2, V1.V3, V1.V4, V2.V3, V2.V4, V3.V4`

. If`order = 'second'`

, the result will be then`V1.V2, V1.V3, V2.V3, V1.V4, V2.V4, V3.V4`

.- FUN
The function that will be applied to each combination. The default is

`+`

, i.e., V1 + V2.- verbose
Logical argument. If

`verbose = FALSE`

the code will run silently.

## Value

A data frame containing all possible combination of variables. Each
combination is the result of the function in `FUN`

applied to the two
variables.

## Author

Tiago Olivoto tiagoolivoto@gmail.com

## Examples

```
# \donttest{
library(metan)
data <- data.frame(A = rnorm(n = 5, mean = 10, sd = 3),
B = rnorm(n = 5, mean = 120, sd = 30),
C = rnorm(n = 5, mean = 40, sd = 10),
D = rnorm(n = 5, mean = 1100, sd = 200),
E = rnorm(n = 5, mean = 2, sd = 1))
comb1 <- comb_vars(data)
comb2 <- comb_vars(data, FUN = '*', order = 'second')
# }
```