mattparker-wf

# Source: the masterful Marc Schwartz, in this R-help thread:
# http://r.789695.n4.nabble.com/previous-monday-date-td3786395.html

# Getting the Monday preceding any date
# See ?cut.Date for additional info
as.Date(cut(Sys.Date(), breaks = "weeks"))

# Alternatively, the preceding Sunday:
as.Date(cut(Sys.Date(), breaks = "weeks", start.on.monday = FALSE)

mattparker-wf

# An alternative approach
# First - a quick function for counting unique values that excludes NAs

count.unique <- function(x) { length(unique(x[!is.na(x)])) }

# Compare:
length(unique(NA))
count.unique(NA)