Question

I have a dataframe where the dates are given as hydrological years (October to September). To change this I am trying to use a if statement:

if(cet$month== 10|cet$month==11|cet$month==12) 
  cet$year <- substr(as.character(cet[,2]),1,4) else
  cet$year <- substr(as.character(cet[,2]),6,9)

but I get an error:
the condition has length > 1 and only the first element will be used

Reading the “if” help file I realized that the condition has to be a length-one logical vector. Is there no way of using an “or” with an “if”? All I want is to apply that expression if the month is October, November or December.

Answer 1

ifelse is the vectorised version. You can also use %in% to reduce the number of statements.

cet$year <- ifelse(cet$month%in%(10:12), substr(as.character(cet[,2]),1,4), substr(as.character(cet[,2]),6,9))