http://d.puremagic.com/issues/show_bug.cgi?id=6004

           Summary: std.range.unzip()
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: Phobos
        AssignedTo: nobody@puremagic.com
        ReportedBy: bearophile_hugs@eml.cc


--- Comment #0 from bearophile_hugs@eml.cc 2011-05-15 05:15:06 PDT ---
In Python and Haskell there is a way to invert the operation of zip(), this is a commonly used feature/function:

Python (V2.6.6):

>>> s = "abc"
>>> d = [1, 2, 3]
>>> z = zip(s, d)
>>> z
[('a', 1), ('b', 2), ('c', 3)]
>>> zip(*z)
[('a', 'b', 'c'), (1, 2, 3)]



Haskell (GHCI v.7.0.2):

Prelude> let s = "abc"
Prelude> let d = [1, 2, 3]
Prelude> let z = zip s d
Prelude> z
[('a',1),('b',2),('c',3)]
Prelude> unzip z
("abc",[1,2,3])



A D example shows where it's useful:

import std.stdio, std.typecons, std.algorithm, std.range;

Tuple!(int,int) divMod(int n, int m) {
    return tuple(n / m, n % m);
}

void main() {
    auto r = map!((m){ return divMod(20,m); })(iota(1, 20));
    int[] firsts, seconds;
    foreach (t; r) {
        firsts ~= t[0];
        seconds ~= t[1];
    }
    writeln(firsts);
    writeln(seconds);
}


Output:
[20, 10, 6, 5, 4, 3, 2, 2, 2, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1]
[0, 0, 2, 0, 0, 2, 6, 4, 2, 0, 9, 8, 7, 6, 5, 4, 3, 2, 1]


Similar code in Python shell:

>>> r = (divmod(20, m) for m in xrange(1,20))
>>> firsts, seconds = zip(*r)
>>> firsts
(20, 10, 6, 5, 4, 3, 2, 2, 2, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1)
>>> seconds
(0, 0, 2, 0, 0, 2, 6, 4, 2, 0, 9, 8, 7, 6, 5, 4, 3, 2, 1)


In Phobos a higher-order function to perform this operation may be named "unzip" as in Haskell. This unzip is generalizable to zips of more than two sequences:

unzip(zip([1,2,3], "abc", [0.5,1.0,1.5]))

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