## digitalmars.D.learn - Cartesian product of ranges?

- Justin Whear <justin economicmodeling.com> Dec 14 2011
- bearophile <bearophileHUGS lycos.com> Dec 14 2011
- bearophile <bearophileHUGS lycos.com> Dec 14 2011
- Philippe Sigaud <philippe.sigaud gmail.com> Dec 14 2011
- Timon Gehr <timon.gehr gmx.ch> Dec 14 2011
- Peter Alexander <peter.alexander.au gmail.com> Jan 01 2012

I've looked through std.algorithm and std.range, but haven't found anything to compute the Cartesian product of several ranges. I have the nagging feeling that this can be accomplished by combining several of the range transformations in the standard library. What I'm after is something like this: alias Tuple!(int, string) P; assert(equal( cartesianProduct([1, 2], ["a", "b"]), [ P(1, "a"), P(1, "b"), P(2, "a"), P(2, "b") ] ));

Dec 14 2011

Justin Whear:alias Tuple!(int, string) P; assert(equal( cartesianProduct([1, 2], ["a", "b"]), [ P(1, "a"), P(1, "b"), P(2, "a"), P(2, "b") ] ));

See std.range.lockstep and std.range.zip. Bye, bearophile

Dec 14 2011

See std.range.lockstep and std.range.zip.

This suggestion was wrong, sorry. There is a need for a product in std.range, I think. Bye, bearophile

Dec 14 2011

On Wed, Dec 14, 2011 at 21:14, Justin Whear <justin economicmodeling.com> w= rote:I've looked through std.algorithm and std.range, but haven't found anythi=

to compute the Cartesian product of several ranges. I have the nagging feeling that this can be accomplished by combining several of the range transformations in the standard library. What I'm after is something like this: alias Tuple!(int, string) P; assert(equal( =C2=A0 =C2=A0 =C2=A0 =C2=A0cartesianProduct([1, 2], ["a", "b"]), =C2=A0 =C2=A0 =C2=A0 =C2=A0[ P(1, "a"), P(1, "b"), P(2, "a"), P(2, "b") ] ));

I needed something like that a year or so ago. You can find it under the name 'combinations' : http://svn.dsource.org/projects/dranges/trunk/dranges/docs/algorithm.html Philippe

Dec 14 2011

On 12/14/2011 09:14 PM, Justin Whear wrote:I've looked through std.algorithm and std.range, but haven't found anything to compute the Cartesian product of several ranges. I have the nagging feeling that this can be accomplished by combining several of the range transformations in the standard library. What I'm after is something like this: alias Tuple!(int, string) P; assert(equal( cartesianProduct([1, 2], ["a", "b"]), [ P(1, "a"), P(1, "b"), P(2, "a"), P(2, "b") ] ));

auto cartesianProduct(R,S)(R r, S s)if(isInputRange!R && isForwardRange!S){ struct CartesianProduct{ private{R r; S s, startS;} this(R r, S s){this.r=r; this.s=s; startS=this.s.save;} property auto front(){return tuple(r.front, s.front);} property bool empty(){return r.empty;} void popFront(){ s.popFront(); if(s.empty){ s = startS.save; r.popFront(); } } static if(isForwardRange!R): property auto save(){return typeof(this)(r.save, s.save);} } return CartesianProduct(r,s); }

Dec 14 2011

On 14/12/11 9:21 PM, Timon Gehr wrote:On 12/14/2011 09:14 PM, Justin Whear wrote:I've looked through std.algorithm and std.range, but haven't found anything to compute the Cartesian product of several ranges. I have the nagging feeling that this can be accomplished by combining several of the range transformations in the standard library. What I'm after is something like this: alias Tuple!(int, string) P; assert(equal( cartesianProduct([1, 2], ["a", "b"]), [ P(1, "a"), P(1, "b"), P(2, "a"), P(2, "b") ] ));

auto cartesianProduct(R,S)(R r, S s)if(isInputRange!R && isForwardRange!S){ struct CartesianProduct{ private{R r; S s, startS;} this(R r, S s){this.r=r; this.s=s; startS=this.s.save;} property auto front(){return tuple(r.front, s.front);} property bool empty(){return r.empty;} void popFront(){ s.popFront(); if(s.empty){ s = startS.save; r.popFront(); } } static if(isForwardRange!R): property auto save(){return typeof(this)(r.save, s.save);} } return CartesianProduct(r,s); }

The implementation of this was discussed at length a while ago. The obvious implementation that you have above was presented, but Andrei was unhappy that it didn't work well with infinite ranges. Some schemes were investigated so that the products of two infinite ranges could would get better sampling, but the whole thing got stuck in analysis paralysis and nothing ever happened. What you have above should be added into Phobos. If people want the product of infinite ranges then they can just to it manually.

Jan 01 2012