Subset function for `<birthdays>` with downgrade-on-subsetting

IF the subsetting invalidates the class then a `<data.frame>` will be returned.

Usage

# S3 method for birthdays
[(x, ...)

Arguments

x

A `birthdays` object

...

further arguments to be passed to or from other methods.

Value

Either a `birthdays` object or a `data.frame`