Question

I have 2 columns of data with the same type of data (Strings).

I want to join the levels of the columns. ie. we have:

col1   col2
Bob    John
Tom    Bob
Frank  Jane
Jim    Bob
Tom    Bob
...    ... (and so on)

now col1 has 4 levels (Bob, Tom Frank, Jim) and col2 has 3 levels (John, Jane, Bob)

But I want both columns to have all the factor levels (Bob, Tom, Frank, Jim, Jane, John), as to later replace each of the ‘names’ with a unique id, such that the final output would be:

col1   col2
1      5
2      1
3      6
4      1
2      1

that is Bob -> 1, Tom -> 2, etc. in both columns.

Any ideas 🙂 ?

edit: Thanks all for the wonderful answers! You are all awesome as far as I know 🙂

Answer 1

You want the factors to include all the unique names from both columns.

col1 <- factor(c("Bob", "Tom", "Frank", "Jim", "Tom"))
col2 <- factor(c("John", "Bob", "Jane", "Bob", "Bob"))
mynames <- unique(c(levels(col1), levels(col2)))
fcol1 <- factor(col1, levels = mynames)
fcol2 <- factor(col2, levels = mynames)

EDIT: a little nicer if you replace the third line with this:

mynames <- union(levels(col1), levels(col2))