Creating a new column to a data frame using a formula from another variable

Question

I want to create a new column to a data frame using a formula from another variable.
Example:
I have a data set \"aa\" is;

x    y 
2    3 
4             


        

Answer 1

If you want to evaluate an expression in the context, of a data frame, you can use with and within.

aa$z <- with(aa, x + y - 2)

or

aa <- within(aa, z <- x + y - 2)

Or, if your expression is in the form of a text string (you should see if there are other ways to write your code; evaluating arbitrary text strings can lead to lots of problems):

aa$z <- eval(parse(text="x + y - 2"), aa)