adding a column in R to a dataframe

Question

How do I add a column to a dataframe in R based on values in another column of a dataframe ?

For eg if I have one column as x$n = [1,2,3,4,5,6] (values in other colums dont exactly matter. And I want another column as a 'category' column that assigns value 0 if x$n < 2, 1 if x$n is between 3 and 4 and 3 if x$n > 4. So that my corresponding column would be x$category = [0,0,1,1,2,2]

Answer 1

Using cut:

within(x, category <- as.integer(cut(n,c(-Inf,2,4,Inf)))-1)

Using ifelse:

within(x, category <- ifelse(n>4, 2, ifelse(n>2, 1, 0)))

Using implicit boolean -> integer coercion::

within(x, category <- (n>2) + (n>4))

Answer 2

If you have:

x = data.frame(n = 1:6)

and only have three categories, then the easiest solution would be:

x$category = 0
x$category[x$n > 2] = 1
x$category[x$n > 4] = 2

If you want to be really clever, then you could do:

x$category = floor(x$n/2.5)

The floor function` just rounds down.