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: nob...@puremagic.com
ReportedBy: bearophile_h...@eml.cc
--- Comment #0 from bearophile_h...@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]))
--
Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email
------- You are receiving this mail because: -------
