An output data type could be one of the many available data types in R, and you could organize the output into a different data structure. For example, the output of this function can be returned as a list of two named elements by creating the function as follows:

    meanSe <- function(numVec){
      if(is.numeric(numVec) & is.vector(numVec)){
        avg <- mean(numVec)
        std <- sd(numVec)
        se <- std/sqrt(length(numVec))
        out <- list(mean = avg, standardError = se)
        return(out)
     }
    }