Cut function returns NA for intervals

Question

I am trying to use the cut function to create age intervals. Unfortunately, I receive NAs for values that match the lower end of the first break.

For example:

AGE <- sample(18:50, 100, replace = TRUE)
AGE_GROUPS <- cut(AGE, breaks = c(18, 27, 36, 45))
DF <- data.frame(AGE, AGE_GROUPS)

For all the values where AGE is 18 and above 45, I receive NA in the AGE_GROUPS variable. How can I make sure that the lowest bracket in AGE_GROUPS includes 18 and how can I make sure that the highest bracket includes all values >= 45?

Answer 1

Breaks isn't just the intermediate breaks, it is the endpoints too. You can make sure you get everything with

breaks = c(-Inf, 18, 27, 36, 45, Inf)

A little more conservatively, you could use

breaks = c(0, 18, 27, 36, 45, 120)

which can be useful for catching outlier coding errors. You may also want include.lowest = TRUE. See ?cut for examples.