Using do loops in R to create new variables

Question

I\'m a long time SAS programmer looking to make the jump to R. I know R isn\'t all that great for variable re-coding but is there a way to do this with do loops.

If

Answer 1

SAS uses a rudimentary macro language, which depends on text replacement rather than evaluation of expressions like any proper programming language. Your SAS files are essentially two things: SAS commands, and Macro expressions (things starting with '%'). Macro languages are highly problematic and hard to debug (for example, do expressions within expressions get expanded? Why do you have to do "&&x" or even "&&&x"? Why do you need two semicolons here?). It's clunky, and inelegant compared to a well-designed programming language that is based on a single syntax.

If your a_i variables are single numbers, then you should have made them as a vector - e.g:

> a = 1:100
> b = runif(100)

Now I can get elements easy:

> a[1]

and add up in parallel:

> c = a + b

You could do it with a loop, initialising c first:

> c = rep(0,100)
> for(i in 1:100){
   c[i]=a[i]+b[i]
   }

But that would be sloooooow.

Nearly every R beginner asks 'how do I create a variable a_i for some values of i', and then shortly afterwards they ask how to access variable a_i for some values of i. The answer is always to make a as either a vector or a list.