I would like to convert a charter sequence into a numeric sequence.
My variable is called labCancer and is made like this:
labCancer
[1] M M M M M M M M M M M M M M M M M M M B B B M M M M M M M M M M M M M M M B
I would like to have:
[1] 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0 1 1 1 1 1 1 1 1 1 1 0
I tried using
labCancer_2 <- labCancer
for (i in 1:569) {
if (labCancer[i] == "M") {
labCancer_2[i] <- 1
} else {
labCancer_2[i] <- 2
} }
but it doesn't work.
Andrea
The only reason I can think of that would cause that loop to not work is failure to initialize labCancer_2. So you would want to do this prior to starting your loop:
labCancer_2 <- numeric(length(labCancer))
If you want to assign to an object element by element in a loop, you need to initialize that object first, or it needs to otherwise exist in some manner.
However, there is a better way to do this that would not require initialization and would be the way many would argue you should do it in R
labCancer_2 <- ifelse(labCancer == "M", 1, 0)
This takes advantage of R's vectorization.
Depending on what you are using the data for, as long as you only have two values, you can do this:
labCancer_2 <- ifelse(lab_cancer=="M", 1, 0)
If you have multiple values or you want to keep the letters around for reference or graphing, you can make the vector a factor:
labCancer_2 <-factor(lab_cancer, levels=c("B", "M"))
However, the factor begins with 1, so your vector would be
2 2 2 2 ... 1 1 1 ...
rather than
1 1 1 1 ... 0 0 0...
One solution would be to convert your vector to a factor, and then to an integer. This will result in all unique values of your original vector to get a separate integer number:
> x <- c("m", "b", "m", "b")
> x
[1] "m" "b" "m" "b"
> as.factor(x)
[1] m b m b
Levels: b m
> as.integer(as.factor(x))
[1] 2 1 2 1
> c(0, 1)[as.numeric(as.factor(x))]
[1] 1 0 1 0
Using the trick in the last line one can easily change the numbers to match 0 and 1.
create a numeric vector (0,1,0,0,1,1), change it to a vector of characters ("0","1","0","0","1","1")
