I have a dataframe with a factor in it, such as:
> var1 <- gl(10, 2, labels=letters[1:10])
> var2 <- c(1:20)
> data <- data.frame(var1=var1,var2=var2)
> data
var1 var2
1 a 1
2 a 2
3 b 3
4 b 4
5 c 5
6 c 6
7 d 7
...
20 j 20
I'm trying to generate a dichotomous variable defined as 1 and 0 for specific values of var1. However, when I enter the following code:
> data <- data.frame(var1=var1,var2=var2)
> data$var3 <- c(1[which(var1=="a" | var1=="b" | var1=="c" | var1=="d" |
var1=="e")], 0[which(var1=="f" | var1=="g" | var1=="h" | var1=="i" | var1=="j")])
I get the following:
> data$var3
[1] 1 NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA
The first item is changed to a 1, but the rest become NAs. How can I obtain the results that I want?
I'm not sure that I even understand how you expected your code to function, but it seems like you just want to create a vector of 1 for values from var1 that are either a, b, c, d, or e, and 0 for the rest. If that's the case, then simply use %in%, which will create a logical vector, and wrap that in as.numeric to convert it to 1s and 0s.
Example:
data$var3 <- as.numeric(data$var1 %in% c("a", "b", "c", "d", "e"))
## Or, shorter:
## data$var3 <- as.numeric(data$var1 %in% letters[1:5])
> head(data, 3)
var1 var2 var3
1 a 1 1
2 a 2 1
3 b 3 1
> tail(data, 3)
var1 var2 var3
18 i 18 0
19 j 19 0
20 j 20 0