First, "==" is logical comparison, so if you want to create a variable based
on both "age" and "group" you can do that. However, it looks like you want
to define the variable "group", so you want to use "<-" or "=" for that.
Second, if you're typing this at a command prompt, you need to make sure you
tell R you're not finished when it looks like you could be. There are
several ways to do this. One is to put everything inside braces; another is
to deliberately leave lines incomplete, like
if (age <= 10) {
group <- 1
} else {
if (age <= 20) {
group <- 2
} else group <- 3
}
Third, this will work for a vector of length 1. If you want to take a vector
"age" and produce a corresponding vector "group", you'll need to put this in
a loop, or use "lapply", or some iteration.
Fourth, you can also write the above as
group <- if (age <= 10) 1 else if (age <= 20) 2 else 3
that is, if() returns a value you can assign.
Finally, besides "ifelse" you can use "cut" for this particular task.
Reid Huntsinger
-----Original Message-----
From: r-help-bounces at stat.math.ethz.ch
[mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of Carlos Maur??cio
Cardeal Mendes
Sent: Tuesday, September 13, 2005 9:29 AM
To: r-help at stat.math.ethz.ch
Subject: [R] if() command
Hi everyone !
Could you please help me with this problem ?
I??ve trying to write a code that assign to a variable the content from
another, but all I??ve got is a message error. For example:
if (age <=10) {group == 1}
else if (age > 10 & age <= 20) {group == 2}
else {group == 3}
Syntax error
Or
if (age <=10) {group == 1}
else (age > 10 & age <= 20) {group == 2}
else {group == 3}
Syntax error
I know that is possible to find the solution by ifelse command or even
recode command, but I??d like to use this way, because I can add another
variable as a new condition and I believe to expand the possibilites.
Thanks,
Mauricio