This function takes a vector with cluster labels and sorts it by frequency
such that the most frequent cluster is the first one and so on.

`sort_clusters(clusters, map_subset = NULL)`

## Arguments

- clusters
A vector with cluster labels.

- map_subset
A logical vector of length equal to `clusters`

specifying
which elements of `clusters`

to use to determine the ranking of the clusters.

## Value

A factor of length equal to `clusters`

where the levels are the new
ordered clusters and the names of the factor are the original values from
`clusters`

.

## Examples

```
## Build an initial set of cluster labels
clus <- letters[unlist(lapply(4:1, function(x) rep(x, x)))]
## In this case, it's a character vector
class(clus)
#> [1] "character"
## Sort them and obtain a factor
sort_clusters(clus)
#> d d d d c c c b b a
#> 1 1 1 1 2 2 2 3 3 4
#> Levels: 1 2 3 4
```