# dummy

From lme4 v1.1-21
by Ben Bolker

##### Dummy variables (experimental)

Largely a wrapper for `model.matrix`

that
accepts a factor, `f`

, and returns a dummy
matrix with `nlevels(f)-1`

columns (the first
column is dropped by default). Useful whenever one wishes to avoid
the behaviour of `model.matrix`

of always returning
an `nlevels(f)`

-column matrix, either by the
addition of an intercept column, or by keeping one
column for all levels.

##### Usage

`dummy(f, levelsToKeep)`

##### Arguments

- f
An object coercible to

`factor`

.- levelsToKeep
An optional character vector giving the subset of

`levels(f)`

to be converted to dummy variables.

##### Value

A `model.matrix`

with dummy variables as columns.

##### Examples

```
# NOT RUN {
data(Orthodont,package="nlme")
lmer(distance ~ age + (age|Subject) +
(0+dummy(Sex, "Female")|Subject), data = Orthodont)
# }
```

*Documentation reproduced from package lme4, version 1.1-21, License: GPL (>= 2)*

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