`frequency_weights()`

creates a vector of frequency weights which allow you
to compactly repeat an observation a set number of times. Frequency weights
are supplied as a non-negative integer vector, where only whole numbers are
allowed.

## Examples

```
# Record that the first observation has 10 replicates, the second has 12
# replicates, and so on
frequency_weights(c(10, 12, 2, 1))
#> <frequency_weights[4]>
#> [1] 10 12 2 1
# Fractional values are not allowed
try(frequency_weights(c(1.5, 2.3, 10)))
#> Error in frequency_weights(c(1.5, 2.3, 10)) :
#> Can't convert `x` <double> to <integer>.
```