Convert continuous numeric values to discrete categories defined by intervals

Question

I have a data frame with a continuous numeric variable, age in months (age_mnths). I want to make a new discrete variable, with age categories based on age intervals.

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Answer 1

rota2$age_gr<-c( "0-5 mnths", "6-11 mnths", "12-23 mnths", "24-59 mnths", "5-14 yrs",
                 "adult")[
           findInterval(rota2$age_mnth , c(-Inf, 5.5, 11.5, 23.5, 59.5, 166.5, Inf) ) ]

Answer 2

If there is a reason you don't want to use cut then I don't understand why. cut will work fine for what you want to do

# Some example data
rota2 <- data.frame(age_mnth = 1:170)
# Your way of doing things to compare against
rota2$age_gr<-ifelse(rota2$age_mnth<6,rr2<-"0-5 mnths",
                     ifelse(rota2$age_mnth>5&rota2$age_mnth<12,rr2<-"6-11 mnths",
                            ifelse(rota2$age_mnth>11&rota2$age_mnth<24,rr2<-"12-23 mnths",
                                   ifelse(rota2$age_mnth>23&rota2$age_mnth<60,rr2<-"24-59 mnths",
                                          ifelse(rota2$age_mnth>59&rota2$age_mnth<167,rr2<-"5-14 yrs",
                                                 rr2<-"adult")))))

# Using cut
rota2$age_grcut <- cut(rota2$age_mnth, 
                       breaks = c(-Inf, 6, 12, 24, 60, 167, Inf), 
                       labels = c("0-5 mnths", "6-11 mnths", "12-23 mnths", "24-59 mnths", "5-14 yrs", "adult"), 
                       right = FALSE)