Martin Maechler <[EMAIL PROTECTED]> writes:
> >> a <- list(b=5)
> >> a[['b']]
> Herve> [1] 5
> >> a[[t<-'b']]
>
> Herve> Nothing gets printed!
>
> Yes, but that is not really much related to "[["
> but rather to "<-" which momentarily turns off auto-printing.
Yes, not being related to "[[" is exactly why it is surprising.
I would expect vv[[f(x)]] to print regardless of f's auto-printing
behavior.
f1 <- function(x) x
f2 <- function(x) return(invisible(x))
a <- list(b=5)
a[[f1("a")]]
a[[f2("a")]]
> Similar things happen in many similar circumstances.
Here's a similar thing:
> v <- 1:5
> v
[1] 1 2 3 4 5
> v[mustBeDocumentedSomewhere=3]
[1] 3
And this can be confusing if one thinks that subsetting is really a
function and behaves like other R functions w.r.t. to treatment of
named arguments:
> m <- matrix(1:4, nrow=2)
> m
[,1] [,2]
[1,] 1 3
[2,] 2 4
> m[j=2]
[1] 2
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