Function to repeat the first level of a factor n times and
return this vector as a factor with the original levels intact

## Usage

`rep_first_factor_value(f, n)`

## Arguments

- f
a factor

- n
numeric; the number of times to repeat the first level of `f`

## Value

A factor of length `n`

with the levels of `f`

, but whose elements
are all the first level of `f`

.