@callback label_for(String.t()) :: String.t()

Often, the column values that divide your partition metrics into groups will be simple keys, and not something that is human readable. Or, if you are displaying a partition metric grouped by a column that is a boolean, Teal will display labels as "false" and "true". For this reason, Teal provides the label_for/1 callback that can be overriden on a partition metric to provide a custom label for each value.

@impl true
def label_for(false), do: "User"
def label_for(true), do: "Admin"

It's also useful for handling null values:

@impl true
def label_for(null), do: "None"
def label_for(key), do: String.capitalize(key)