On Friday, 13 February 2015 at 18:32:35 UTC, Andrei Alexandrescu
wrote:
* Perhaps rename groupBy to chunkBy. People coming from SQL and
other languages might expect groupBy to do hash-based grouping.
Agreed.
* The unary function implementation must return for each group
a tuple consisting of the key and the lazy range of values. The
binary function implementation should continue to only return
the lazy range of values.
Is the purpose of this just to avoid the user potentially needing
to evaluate the key function twice?
* SortedRange should add a method called group(). Invoked with
no predicate, group() should do what chunkBy does, using the
sorting predicate.
Will need to be called something else since there may be existing
code trying to call std.algorithm.group using UFCS. This would
change its behaviour.
* aggregate() should detect the two kinds of results per group
(well, chunk) and process them accordingly: for unary-predicate
chunks, pass the key through and only process the lazy range.
Meaning:
auto data = [
tuple("John", 100),
tuple("John", 35),
tuple("Jane", 200),
tuple("Jane", 87),
];
auto r = data.chunkBy!(x => x[0]).aggregate!sum;
yields a range of tuples: tuple("John", 135), tuple("Jane",
187).
Not sure I understand how this is meant to work.
With your second bullet implemented, data.chunkBy!(x => x[0])
will return:
tuple("John", [tuple("John", 100), tuple("John", 35)]),
tuple("Jane", [tuple("Jane", 200), tuple("Jane", 87)])
(here [...] denotes the sub-range, not an array).
So aggregate will ignore the key part, but how does it know to
ignore the name in sub-ranges?
