How to replace character stringers with numeric indices

Question

How would you replace character strings with numeric values?

For example, suppose I have a vector like so,

n <- c(rep("Sam", 3), "Harry", rep("Sparky", 2), rep("Ted", 4), "Red")

>n
 [1] "Sam"    "Sam"    "Sam"    "Harry"  "Sparky" "Sparky" "Ted"    "Ted"    "Ted"   
[10] "Ted"    "Red"

I would like to get an output like this,

 [1] 1 1 1 2 3 3 4 4 4 4 5

Where

• Sam is indexed by 1
• Harry is indexed by 2
• Sparky by 3
• Ted by 4
• Red by 5.

Answer 1

Here a solution using factor approach preserving desired order:

n <- factor(n, levels = unique(n))
> as.numeric(n)
 [1] 1 1 1 2 3 3 4 4 4 4 5

Answer 2

We can use match

match(n, unique(n))
#[1] 1 1 1 2 3 3 4 4 4 4 5