*在R中是什么意思？

Question

For instance:

> TRUE * 0.5
   0.5
> FALSE * 0.5
   0

I don't know if the secret here is the * character itself or the way R encodes logical statements, but I can't understand why the results.

Answer 1

R has a fairly loose type system and rather freely does coercion, hopefully when it is sensible. When coerced to numeric by * , logical values become 0 (FALSE) and 1 (TRUE), your expression gets evaluated with the usual mathematical convention of all values times 0 equal 0, and all values times 1 equal the value. The one exception to that rule in the numeric domain is Inf * 0 returns NaN . Character values have no "destination"-type when composed with "*", so "1"*TRUE throws an error.