[Rd] undocumented name mangling during unlist?
sfalcon at fhcrc.org
Tue Jan 9 18:43:51 CET 2007
Prof Brian Ripley <ripley at stats.ox.ac.uk> writes:
> On Mon, 8 Jan 2007, Seth Falcon wrote:
>> The documentation for unlist says:
>> By default, 'unlist' tries to retain the naming information
>> present in 'x'. If 'use.names = FALSE' all naming information is
>> Hence, I find it odd that I see the following:
>> > b <- list("highway1"=1:5)
>> > unlist(b)
>> highway11 highway12 highway13 highway14 highway15
>> 1 2 3 4 5
>> I suspect this is essential behavior for something or other, but it
>> seems that this approach is inefficient for large lists and in many
>> contexts does not preserve names, but invents new ones.
> There is the information that the entries came from element "highway1"
> which needs to be preserved.
In my view, preserving is not the same as creating a new name where
the original is a substring.
> c() and unlist() share code, and both try to create different names
> for elements of different origin.
I guess I don't understand. In my example, aren't the elements all of
the same origin (from the highway1 entry of the list)?
Granting a different interpretation of origin, it seems the attempt is
not very complete:
v2 <- list(a=rep(1, 2), b=rep(2, 2), a=rep(3, 2))
unlist(v2) ## names are _not_ unique
a1 a2 b1 b2 a1 a2
1 1 2 2 3 3
> Why is this 'inefficient' (names are optional) and what do you
> propose that meets the conditions?
Could the origin name simply be repeated?
highway1 highway1 highway1 highway1 highway1
1 2 3 4 5
Efficiency could be gained by reusing the CHARSXP to name all elements
instead of having to created new strings for each name.
More information about the R-devel