I see cartesianProduct in std.algorithm. I read:

auto N = sequence!"n"(0); // the range of natural numbers
auto N2 = cartesianProduct(N, N); // the range of all pairs of natural numbers

So it gives (0,0) (0,1) (1,0) ... and so on.

Is there a way to generate only tuple:

a[0] > a[1] (0,1) (0,2) ... (1,2) (1,3) .. (2,3) (2,4)

or

a[0] >= a[1] (0,0) (0,1) (0,2) ... (1,1) (1,2) (1,3) .. (2,2) (2,3) (2,4)

Or the only way is use filter!(...) after cartesianProduct?

On Thursday, 28 February 2013 at 15:32:00 UTC, Andrea Fontana wrote:
> I see cartesianProduct in std.algorithm. I read:
>
> auto N = sequence!"n"(0); // the range of natural numbers
> auto N2 = cartesianProduct(N, N); // the range of all pairs of natural numbers
>
> So it gives (0,0) (0,1) (1,0) ... and so on.
>
> Is there a way to generate only tuple:
>
> a[0] > a[1] (0,1) (0,2) ... (1,2) (1,3) .. (2,3) (2,4)
>
> or
>
> a[0] >= a[1] (0,0) (0,1) (0,2) ... (1,1) (1,2) (1,3) .. (2,2) (2,3) (2,4)
>
> Or the only way is use filter!(...) after cartesianProduct?

PS: In my case I can't use filter!(...): I'm trying to compare an array of struct with itself to find similar ones, so I can't filter Tuple(struct, struct) in any way...

I have to write:

for (i; 0..arr.length) for(j; i+1..arr.length) // check arr[i] and arr[j] for similarities

Any ideas?

Andrea Fontana:

> Any ideas?

I suggested pairwise():
http://d.puremagic.com/issues/show_bug.cgi?id=6788

Bye,
bearophile

On Thu, Feb 28, 2013 at 04:31:59PM +0100, Andrea Fontana wrote:
> I see cartesianProduct in std.algorithm. I read:
> 
> auto N = sequence!"n"(0); // the range of natural numbers
> auto N2 = cartesianProduct(N, N); // the range of all pairs of
> natural numbers
> 
> So it gives (0,0) (0,1) (1,0) ... and so on.
> 
> Is there a way to generate only tuple:
> 
> a[0] > a[1] (0,1) (0,2) ... (1,2) (1,3) .. (2,3) (2,4)
[...]

auto triangularProduct(R1,R2)(R1 r1, R2 r2)
	if (isForwardRange!R1)
{
	return map!(function(a) => zip(take(a[1].save, a[0]), repeat(a[2])))(
			zip(sequence!"n"(0), repeat(r1.save), r2)
		)
		.joiner();
}

Both ranges can be infinite, only the first one needs to be a forward range.


> a[0] >= a[1] (0,0) (0,1) (0,2) ... (1,1) (1,2) (1,3) .. (2,2) (2,3)
> (2,4)
[...]

auto triangularProduct2(R1,R2)(R1 r1, R2 r2)
	if (isForwardRange!R1)
{
	return map!(function(a) => zip(take(a[1].save, a[0]), repeat(a[2])))(
			zip(sequence!"n"(1), repeat(r1.save), r2)
		)
		.joiner();
}

As above, both ranges can be infinite, only the first one needs to be a forward range.

Hope this helps. ;-)


T

-- 
Gone Chopin. Bach in a minuet.

On Thursday, 28 February 2013 at 18:23:04 UTC, H. S. Teoh wrote:
> On Thu, Feb 28, 2013 at 04:31:59PM +0100, Andrea Fontana wrote:
>> I see cartesianProduct in std.algorithm. I read:
>> 
>> auto N = sequence!"n"(0); // the range of natural numbers
>> auto N2 = cartesianProduct(N, N); // the range of all pairs of
>> natural numbers
>> 
>> So it gives (0,0) (0,1) (1,0) ... and so on.
>> 
>> Is there a way to generate only tuple:
>> 
>> a[0] > a[1] (0,1) (0,2) ... (1,2) (1,3) .. (2,3) (2,4)
> [...]
>
> auto triangularProduct(R1,R2)(R1 r1, R2 r2)
> 	if (isForwardRange!R1)
> {
> 	return map!(function(a) => zip(take(a[1].save, a[0]), repeat(a[2])))(
> 			zip(sequence!"n"(0), repeat(r1.save), r2)
> 		)
> 		.joiner();
> }
>
> Both ranges can be infinite, only the first one needs to be a forward
> range.
>
>
>> a[0] >= a[1] (0,0) (0,1) (0,2) ... (1,1) (1,2) (1,3) .. (2,2) (2,3)
>> (2,4)
> [...]
>
> auto triangularProduct2(R1,R2)(R1 r1, R2 r2)
> 	if (isForwardRange!R1)
> {
> 	return map!(function(a) => zip(take(a[1].save, a[0]), repeat(a[2])))(
> 			zip(sequence!"n"(1), repeat(r1.save), r2)
> 		)
> 		.joiner();
> }
>
> As above, both ranges can be infinite, only the first one needs to be a
> forward range.
>
> Hope this helps. ;-)
>
>
> T

triangulaProduct2 for [0,1,2,3] and [0,1,2,3] doesn't give (0,0) (1,1) (2,2) (3,3)

:)

On Thu, Feb 28, 2013 at 09:20:52PM +0100, Andrea Fontana wrote:
> On Thursday, 28 February 2013 at 18:23:04 UTC, H. S. Teoh wrote:
[...]
> >auto triangularProduct2(R1,R2)(R1 r1, R2 r2)
> >	if (isForwardRange!R1)
> >{
> >	return map!(function(a) => zip(take(a[1].save, a[0]),
> >repeat(a[2])))(
> >			zip(sequence!"n"(1), repeat(r1.save), r2)
> >		)
> >		.joiner();
> >}
> >
> >As above, both ranges can be infinite, only the first one needs to
> >be a
> >forward range.
> >
> >Hope this helps. ;-)
> >
> >
> >T
> 
> triangulaProduct2 for [0,1,2,3] and [0,1,2,3] doesn't give (0,0)
> (1,1) (2,2) (3,3)
> 
> :)

Ahhh, slight mistake there, it should be:

auto triangularProduct2(R1,R2)(R1 r1, R2 r2)
	if (isForwardRange!R1)
{
	return map!(function(a) => zip(take(a[1].save, a[0]+1), repeat(a[2])))(
			zip(sequence!"n"(1), repeat(r1.save), r2)
		)
		.joiner();
}

There, better now? ;-)

Also, if you only need products of finite ranges, it's possible to rewrite it so that it produces items in a nicer order. The strange order output by my examples are to cater for the infinite case.


T

-- 
Life would be easier if I had the source code. -- YHL

On Thu, Feb 28, 2013 at 03:01:48PM -0800, H. S. Teoh wrote:
> On Thu, Feb 28, 2013 at 09:20:52PM +0100, Andrea Fontana wrote:
> > On Thursday, 28 February 2013 at 18:23:04 UTC, H. S. Teoh wrote:
> [...]
> > >auto triangularProduct2(R1,R2)(R1 r1, R2 r2)
> > >	if (isForwardRange!R1)
> > >{
> > >	return map!(function(a) => zip(take(a[1].save, a[0]),
> > >repeat(a[2])))(
> > >			zip(sequence!"n"(1), repeat(r1.save), r2)
> > >		)
> > >		.joiner();
> > >}
> > >
> > >As above, both ranges can be infinite, only the first one needs to
> > >be a
> > >forward range.
> > >
> > >Hope this helps. ;-)
> > >
> > >
> > >T
> > 
> > triangulaProduct2 for [0,1,2,3] and [0,1,2,3] doesn't give (0,0)
> > (1,1) (2,2) (3,3)
> > 
> > :)
> 
> Ahhh, slight mistake there, it should be:
> 
> auto triangularProduct2(R1,R2)(R1 r1, R2 r2)
> 	if (isForwardRange!R1)
> {
> 	return map!(function(a) => zip(take(a[1].save, a[0]+1), repeat(a[2])))(
> 			zip(sequence!"n"(1), repeat(r1.save), r2)
[...]

Argh. Another mistake. The above line should read:

 			zip(sequence!"n"(0), repeat(r1.save), r2)

:-/


T

-- 
Once bitten, twice cry...