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 class 'POSIXlt'
wp_year(timestamp)
## Default S3 method:
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.
providing 
.