> newweekdaynum <- strptime(SFCrimeData$DayOfWeek, "%u")

#some example data
set.seed(42)
x <- factor(sample(c("Monday", "Tuesday", "Wednesday",
                     "Thursday", "Friday", "Saturday", "Sunday"),
            20, TRUE))
# [1] Sunday    Sunday    Wednesday Saturday  Friday    Thursday  Saturday  Monday    Friday    Friday    Thursday  Saturday  Sunday
#[14] Tuesday   Thursday  Sunday    Sunday    Monday    Thursday  Thursday
#Levels: Friday Monday Saturday Sunday Thursday Tuesday Wednesday

#turn into ordered factor
x <- factor(x, levels = c("Monday", "Tuesday", "Wednesday",
                          "Thursday", "Friday", "Saturday", "Sunday"),
            ordered = TRUE)
#[1] Sunday    Sunday    Wednesday Saturday  Friday    Thursday  Saturday  Monday    Friday    Friday    Thursday  Saturday  Sunday
#[14] Tuesday   Thursday  Sunday    Sunday    Monday    Thursday  Thursday
#Levels: Monday < Tuesday < Wednesday < Thursday < Friday < Saturday < Sunday

#extract underlying integer values
as.integer(x)
#[1] 7 7 3 6 5 4 6 1 5 5 4 6 7 2 4 7 7 1 4 4