The code from gram.y that handles this looks like this in R-devel:
/* allow top-level placeholder */
for (SEXP a = CDR(rhs); a != R_NilValue; a = CDR(a))
if (CAR(a) == R_PlaceholderToken) {
if (TAG(a) == R_NilValue)
raiseParseError("placeholderNotNamed", rhs,
NO_VALUE, NULL, lloc_rhs,
_("pipe placeholder can only be used as a
named argument (%s:%d:%d)"));
checkTooManyPlaceholders(rhs, CDR(a), lloc_rhs);
SETCAR(a, lhs);
return rhs;
}
check_rhs(rhs, lloc_rhs);
The "check_rhs" function is the one that complains about using `[` as a
function on the right hand side. So it is never run when there's a
placeholder found. Not sure if this is intentional or not.
You can see more context here:
https://github.com/wch/r-source/blob/0ece3677bc1c4a1c76ecbcff62424d72d742d492/src/main/gram.y#L1248
.
Duncan Murdoch
On 18/07/2022 3:48 p.m., Gabriel Becker wrote:
It looks to me like the 'bug' here seems to be that
aggregate(y ~ f, df1, mean) |> `[`(x = _, 'y')
does not throw the same error as
aggregate(y ~ f, df1, mean) |> `[`('y')
Since the latter seems pretty clear that the intent is that `[` is
disallowed on the RHS of the pipe by design.
~G
On Mon, Jul 18, 2022 at 11:07 AM Toby Hocking wrote:
Is the intent is to encourage the user to do something simpler like...
aggregate(y ~ f, df1, mean)$y
aggregate(y ~ f, df1, mean)["y"]
aggregate(y ~ f, df1, mean)[["y"]]
??
On Sat, Jul 16, 2022 at 8:27 AM Rui Barradas wrote:
Hello,
When piping to any of `[.data.frame` or `[[.data.frame`, the placeholder
in mandatory.
df1 <- data.frame(y = 1:10, f = rep(c("a", "b"), each = 5))
aggregate(y ~ f, df1, mean) |> `[`('y')
# Error: function '[' not supported in RHS call of a pipe
aggregate(y ~ f, df1, mean) |> `[[`('y')
# Error: function '[' not supported in RHS call of a pipe
But if used it throws a warning.
aggregate(y ~ f, df1, mean) |> `[`(x = _, 'y')
# Warning in `[.data.frame`(x = aggregate(y ~ f, df1, mean), "y"):
named arguments
# other than 'drop' are discouraged
#y
# 1 3
# 2 8
aggregate(y ~ f, df1, mean) |> `[[`(x = _, 'y')
# Warning in `[[.data.frame`(x = aggregate(y ~ f, df1, mean), "y"):
named
# arguments other than 'exact' are discouraged
# [1] 3 8
Hasn't this become inconsistent behavior?
More than merely right, the named argument is mandatory, it shouldn't
give warnings.
Hope this helps,
Rui Barradas
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