(Ted Harding) wrote:
On 28-Jul-08 17:52:31, Henrik Bengtsson wrote:
Use '&' for vectors and '&&' for scalars. Ditto applies to the OR
operator(s). /Henrik
What's wrong with using "&" for scalars? Surely it gives the
correct answer? Maybe it's simply a bit slower, or something?
Semantics are subtly different. a && b does not evaluate b if a is FALSE
(it is equivalent to if(a) then b else FALSE), so
> F & print("Hi")
[1] "Hi"
Error in F & print("Hi") :
operations are possible only for numeric or logical types
> F && print("Hi")
[1] FALSE
This is a bit synthetic, but it shows that there are differences in side
effects and error checking. In real life, an important case would be
when "a" is a check that "b" is at all computable.
-p
--
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