Feature request: epi-week

[garrettgman]

I'm an epidemiologist with a focus on acute disease surveillance and often need to plot disease trends by a standard CDC "epi-week." I haven't been able to find an existing function that creates this type of week from a date variable in a data frame, and it's a huge hindrance to transitioning from SAS where we have code for this purpose. The only thing I have found is this discussion:
https://www.linkedin.com/groups/Date-function-in-R-is-77616.S.5875641964430376964
.

More on CDC epi-weeks (for example):
https://ibis.health.state.nm.us/resources/MMWRWeekCalendar.html

[chrismerkord]

This might need to be revisited. See my comment here: #492 (comment)