Logical operators - short (relational) vs long (vector) forms

Question

I am getting a bit confused by the use of the short and long forms of logical operators in R.

If I have the following values

A <- FALSE
B <- TRUE
X <- 3
Y <- 2

I would like to evaluate NOT(A) OR NOT(B) AND X < Y

I expect FALSE given the parameters

This is the expression I have found to evaluate this in R so it returns FALSE as I expect:

!A & X < Y || !B & X < Y

Can I eliminate the repeated X < Y comparison?

... You really should use more parentheses to make it clear what you're trying to do. — Dason, Mar 14 '13 at 16:08

score 5 · Accepted Answer · answered Mar 14 '13 at 16:06

5

Do you mean:

> (!A || !B) && X < Y
[1] FALSE

?

answered Mar 14 '13 at 16:06

NPE

Ah ha. Exactly, thank you. Parentheses. Damn, I should know better! I will accept as soon as the clock runs down. Thanks. – Simon O'Hanlon Mar 14 '13 at 16:08

score 3 · Answer 2 · answered Mar 14 '13 at 16:13

3

short form gives you a vector.
long form gives you a single value. compare:

   x <- c(TRUE, TRUE, FALSE)
   y <- c(TRUE, FALSE, FALSE)


   X && Y
   X & y

   x || y
   x | y

answered Mar 14 '13 at 16:13

Ricardo Saporta

+1 Really nice example of the way the short and long forms work, thanks. – Simon O'Hanlon Mar 14 '13 at 16:18

score 1 · Answer 3 · answered Mar 14 '13 at 16:17

1

Another possibility:

!(A * B) && X < Y

answered Mar 14 '13 at 16:17

Sven Hohenstein

3 Answers3