Function to extract the year from a timestamp of e.g. class POSIXlt, POSIXct, Date, or character. If the option is of type character it should be in the form of yyyy-mm-dd.
Usage
wp_year(timestamp)
# S3 method for POSIXlt
wp_year(timestamp)
# S3 method for default
wp_year(timestamp)
Arguments
timestamp
Some sort of timestamp e.g. of class POSIXlt, POSIXct, Date,
or character. If the option is of type character it should be in the form
of yyyy-mm-dd.