Compare strings with logical operator in R

Question

I'm getting an error trying to compare and set weekday string values as either a "weekend" or a "weekday" using R. Any suggestions on how to approach this problem in a better way would be great.

x <- c("Mon","Tue","Wed","Thu","Fri","Sat","Sun")

setDay <- function(day){
          if(day == "Sat" | "Sun"){
           return("Weekend")
          } else { 
            return("Weekday")
          }
        }

sapply(x, setDay)

This is the error I get back in RStudio:

Error in day == "Sat" | "Sun" : 
  operations are possible only for numeric, logical or complex types

Solution

Instead of using sapply to loop through each individual day in x and check whether it's the weekday or weekend, you can do this in a single vectorized operation with ifelse and %in%:

ifelse(x %in% c("Sat", "Sun"), "Weekend", "Weekday")
# [1] "Weekday" "Weekday" "Weekday" "Weekday" "Weekday" "Weekend" "Weekend"

The motivation for using vectorized operations here is twofold -- it will save you typing and it will make your code more efficient.

Comments

[Frank]

And as a counter to the ifelse hate: c("Weekend", "Weekday")[1L+x %in% c("Sat", "Sun")]

[josliber]

@Frank I understand the motivation for that sort of expression instead of ifelse, but I find it to be a lot less readable.

[Señor O]

^^ especially the 1L - is that even necessary?

[Frank]

I'm with you; just trying to guard against an unnecessary answer with that approach :)

[josliber]

@SeñorO you add the 1 to convert FALSE and TRUE to indices 1 and 2, respectively.

[Señor O]

Yeah, but the L specifies that it's an integer, which is used sometimes in highly optimized code, which this doesn't need to be. I think [1 + x %in% c(...)] would be more readable?

[josliber]

Ah gotcha, you're saying 1L versus 1. I also noticed in this particular case that it should be c("Weekday", "Weekend")[1L+x %in% c("Sat", "Sun")] instead (flip the first vector).

[ExperimenteR]

ifelse("Sunday" %in% c("Sat", "Sun"), "Weekend", "Weekday")

[josliber]

@ExperimenteR well, from the question it seems like it's going to be "Sun" instead of "Sunday" -- note that the OP's original code (with the bug fix) will also return "Weekday" in this case. Of course, you could defend against the fully spelled days by checking for inclusion in the set c("Sat", "Sun", "Saturday", "Sunday").

[rbatt]

also, if %in% syntax confuses you, you can use is.element() (although takes up more characters)

[MichaelChirico]

Once we start allowing Sunday, Saturday, Sat, etc., it's time to regex: ifelse(grepl("sun|sat",tolower(x)),"Weekend","Weekday")

[MichaelChirico]

For the uninitiated, "the motivation for that sort of expression" is here