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March 30, 2015 Mapping with partial | ||||
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Hi again, I have this simple toy code : import point; import std.random; import std.algorithm; import std.functional; void getRandomPoint(R)(R randVar, ref Point p) { p.x = randVar; p.y = randVar; p.z = randVar; } void main() { Point[500] points; auto randVar = uniform(0.0f, 1.0f); alias test = partial!(getRandomPoint, randVar); points.map!(test); } And get the following error : kmeans_example.d(79): Error: template std.algorithm.iteration.map cannot deduce function from argument types !(partial)(Point[500]), candidates are: /usr/include/dmd/phobos/std/algorithm/iteration.d(434): std.algorithm.iteration.map(fun...) if (fun.length >= 1) Btw, I don't understand why : auto test = partial!(getRandomPoint, randVar); dont work...partial doesnt return a delegate it seems...:/ |
March 30, 2015 Re: Mapping with partial | ||||
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Posted in reply to matovitch | (it's not on line 79 obviously, you got me :D) |
March 30, 2015 Re: Mapping with partial | ||||
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Posted in reply to matovitch | On Monday, 30 March 2015 at 18:07:18 UTC, matovitch wrote:
> kmeans_example.d(79): Error: template std.algorithm.iteration.map
That error is easy: use points[].map!(test) instead of points.map.
Since points is a static array, it isn't a range. Static arrays can't be popped through. But if you slice it, then it yields a usable range for map.
The other problem though is the partial!(). It expects a template argument for the thing so it can make a new function right there at compile time... which doesn't work with a runtime variable.
The way I'd do it is just with a little hand written delegate. This will compile, for example:
auto test = (ref Point p) => getRandomPoint(randVar, p);
points[].map!(test);
and should do what you need.
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March 30, 2015 Re: Mapping with partial | ||||
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Posted in reply to Adam D. Ruppe | On Monday, 30 March 2015 at 18:23:32 UTC, Adam D. Ruppe wrote:
> On Monday, 30 March 2015 at 18:07:18 UTC, matovitch wrote:
>> kmeans_example.d(79): Error: template std.algorithm.iteration.map
>
> That error is easy: use points[].map!(test) instead of points.map.
>
> Since points is a static array, it isn't a range. Static arrays can't be popped through. But if you slice it, then it yields a usable range for map.
>
>
> The other problem though is the partial!(). It expects a template argument for the thing so it can make a new function right there at compile time... which doesn't work with a runtime variable.
>
> The way I'd do it is just with a little hand written delegate. This will compile, for example:
>
> auto test = (ref Point p) => getRandomPoint(randVar, p);
> points[].map!(test);
>
>
> and should do what you need.
Nice ! Thanks for the tip ! I tried importing std.range and points.array works too.
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March 30, 2015 Re: Mapping with partial | ||||
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Posted in reply to matovitch | On Monday, 30 March 2015 at 18:29:32 UTC, matovitch wrote:
> I tried importing std.range and points.array works too.
Aye, that would work too, but the slice I think is more efficient as I'm pretty sure... not completely sure, but I think .array makes a copy of static arrays, whereas the slice doesn't.
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March 30, 2015 Re: Mapping with partial | ||||
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Posted in reply to Adam D. Ruppe | On Monday, 30 March 2015 at 18:34:19 UTC, Adam D. Ruppe wrote:
> On Monday, 30 March 2015 at 18:29:32 UTC, matovitch wrote:
>> I tried importing std.range and points.array works too.
>
> Aye, that would work too, but the slice I think is more efficient as I'm pretty sure... not completely sure, but I think .array makes a copy of static arrays, whereas the slice doesn't.
I was going to ask you the question does it just add the range shell or does it make a copy ? :/ Maybe someone else know.
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March 30, 2015 Re: Mapping with partial | ||||
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Posted in reply to Adam D. Ruppe | Well I have a bit of a similar problem with foreach. If I use classic T[] range, I can do : foreach(int i, auto t, myRange)... But if I use an Array!T (from std.container) I get : cannot infer argument types, expected 1 argument, not 2 Even if I add the brackets []. Any idea ? Thanks for your help ! :) |
March 30, 2015 Re: Mapping with partial | ||||
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Posted in reply to matovitch | On Monday, 30 March 2015 at 18:37:53 UTC, matovitch wrote: > On Monday, 30 March 2015 at 18:34:19 UTC, Adam D. Ruppe wrote: [...] >> Aye, that would work too, but the slice I think is more efficient as I'm pretty sure... not completely sure, but I think .array makes a copy of static arrays, whereas the slice doesn't. > > I was going to ask you the question does it just add the range shell or does it make a copy ? :/ Maybe someone else know. Let's check the documentation. http://dlang.org/phobos/std_array.html#array says: "Allocates an array and initializes it with copies of the elements of range r." Documentation says copy. Let's check the actual behaviour. ---- void main() { int[1] a = [1]; import std.array: array; a.array[0] = 2; import std.stdio: writeln; writeln(a[0]); } ---- (also at <http://dpaste.dzfl.pl/1191144a9acf>) This program prints "1". That's the output we'd expect when `array` makes a copy. Actual behaviour says copy. So, copy. |
March 30, 2015 Re: Mapping with partial | ||||
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Posted in reply to anonymous | On Monday, 30 March 2015 at 19:08:24 UTC, anonymous wrote:
> On Monday, 30 March 2015 at 18:37:53 UTC, matovitch wrote:
>> On Monday, 30 March 2015 at 18:34:19 UTC, Adam D. Ruppe wrote:
> [...]
>>> Aye, that would work too, but the slice I think is more efficient as I'm pretty sure... not completely sure, but I think .array makes a copy of static arrays, whereas the slice doesn't.
>>
>> I was going to ask you the question does it just add the range shell or does it make a copy ? :/ Maybe someone else know.
>
> Let's check the documentation. http://dlang.org/phobos/std_array.html#array says: "Allocates an array and initializes it with copies of the elements of range r." Documentation says copy.
>
> Let's check the actual behaviour.
> ----
> void main()
> {
> int[1] a = [1];
> import std.array: array;
> a.array[0] = 2;
> import std.stdio: writeln;
> writeln(a[0]);
> }
> ----
> (also at <http://dpaste.dzfl.pl/1191144a9acf>)
> This program prints "1". That's the output we'd expect when `array` makes a copy. Actual behaviour says copy.
>
> So, copy.
That settle the point for array as for [] ? I guess the documentation should have something to say about it too. ;)
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March 30, 2015 Re: Mapping with partial | ||||
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Posted in reply to matovitch | On Monday, 30 March 2015 at 19:11:10 UTC, matovitch wrote: > That settle the point for array as for [] ? I though that was clear. [] doesn't copy. > I guess the documentation should have something to say about it too. ;) hopefully |
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