[R] How to fix the warning message "the condition has length > 1 and only the first element will be used"?

[jcrosbie]

I'm trying to create a function to return the date x months in the past. 

With the code below I'm getting the warning message:

Warning message:
In if (MonthsBack >= CurrentMonth) { :
  the condition has length > 1 and only the first element will be used


##############################

DateBack <- function(CurrentYear, CurrentMonth, MonthsBack){
        if(MonthsBack< 13){
                if(MonthsBack>=CurrentMonth){
                        month<-12+CurrentMonth-MonthsBack
                        datet<-paste(CurrentYear-1,month, sep="-")
                } 
                else{
                        month<-CurrentMonth-MonthsBack
                        datet<-paste(CurrentYear-1, month, sep="-")
                }
        } 
        else{
                Years <- trunc(MonthsBack/12,0)
                if((MonthsBack-12*Years)>=CurrentMonth){
                        month<-12+CurrentMonth-MonthsBack
                } 
                else{
                        month<-CurrentMonth-MonthsBack
                }
                datet<-paste(CurrentYear-Years, month, sep="-")
        }
return(datet)
}

CurrentYear<- c(2000, 2000, 2003, 2004)
CurrentMonth<-c(1, 2, 6, 12) 

df<- data.frame(CurrentYear, CurrentMonth)

df$MonthsBack <- DateBack(df$CurrentYear,df$CurrentMonth,1)






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