interaction {Hmisc} | R Documentation

## Compute the Interaction of Several Factors

### Description

This is a replacement for the builtin function `interaction` that adds the parameters `sep` and `left`.

### Usage

    interaction(..., drop=FALSE, sep=".", left=FALSE)

### Arguments

`...` | the arguments to `interaction` can be either a data frame containing all the factors to be used all the individual factors. It will not understand a combination of factors and designs as arguments; you have to pick one form or the other.
`drop` | if `TRUE` the levels of the new factor not represented in the data are dropped.
`sep` | the separator in creating the level descriptors.
`left` | set to `TRUE` to left-justify factor levels when constructing label strings

### Details

This is a slight modification of the S-supplied function. The `sep` argument has been added, a sort step has been added to properly sort the levels of the created variable, and the `left` parameter is added.

### Value

a new factor, whose levels are all possible combinations of the factors supplied as arguments. If `drop =TRUE`, only the levels represented in the new factor are retained.

### Examples

    Temp <- c(160, 180, 160, 180, 160, 180, 160, 180)
    Conc <- c(20, 20, 40, 40, 20, 20, 40, 40)
    interaction(Temp, Conc)

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