Understanding when the && operator short circuits [duplicate]

Question

This question already has answers here:

Logical operators (AND, OR) with NA, TRUE and FALSE (2 answers)

Closed 9 years ago.

Perhaps I'm missing something obvious.

In R, TRUE && NA evalues to NA. This doesn't make sense to me, because && should evaluate left to right, and stop as soon as one of its conditions is true.

Answer 1

This doesn't make sense to me, because && should evaluate left to right, and stop as soon as one of its conditions is true.

This is wrong. You are mixing up && with ||:

• TRUE && FALSE gives FALSE
  • && requires both conditions to be TRUE
  • && will short-circuit on FALSE
• TRUE || FALSE gives TRUE
  • || requires a single condition to be TRUE
  • || will short-circuit on TRUE

Also,

TRUE || NA 

gives

TRUE