Hi,

How can expect the output when I subset a vector using a vector of boolean values with different length. For example:

```
a <- c(1,2,3)
b <- c(TRUE,FALSE)
d <- c(FALSE,TRUE)
e <- c(TRUE)
f <- c(FALSE)
a[b]; a[c]; a[d]; a[e]; a[f]
```

Is there any rule for this situation?

Thanks!