I have a range which is the result of a couple of chained range operations, and each element is:

    Tuple!(string, "product", double, "price")

Now I'd like to sort the range by "price" using:

    sort!((pp1, pp2) => cmp(pp1.price,  pp2.price) > 0)(theRange)

But I get a compile time error:

source/services.d(166,63): Error: template std.algorithm.sorting.sort
cannot deduce function from argument types !((pp1, pp2) =>
cmp(pp1.price, pp2.price) > 0)(MapResult!(__lambda5, Result)),
candidates are:
/home/bahman/Programs/D/dmd-2.071.0/linux/bin64/../../src/phobos/std/algorithm/sorting.d(1027,1):
       std.algorithm.sorting.sort(alias less = "a < b", SwapStrategy ss
= SwapStrategy.unstable, Range)(Range r) if ((ss ==
SwapStrategy.unstable && (hasSwappableElements!Range ||
hasAssignableElements!Range) || ss != SwapStrategy.unstable &&
hasAssignableElements!Range) && isRandomAccessRange!Range &&
hasSlicing!Range && hasLength!Range)
source/services.d(168,5): Error: var has no effect in expression (theRange)
dmd failed with exit code 1.

And I have no clue what it is complaining about.  I'd really appreciate any hint/help on this.

Thanks,

-- 
Bahman

On 07/26/2016 09:35 AM, Bahman Movaqar wrote:
> I have a range which is the result of a couple of chained range operations, and each element is:
> 
>     Tuple!(string, "product", double, "price")
> 
> Now I'd like to sort the range by "price" using:
> 
>     sort!((pp1, pp2) => cmp(pp1.price,  pp2.price) > 0)(theRange)
> 
> But I get a compile time error:
> 
> source/services.d(166,63): Error: template std.algorithm.sorting.sort
> cannot deduce function from argument types !((pp1, pp2) =>
> cmp(pp1.price, pp2.price) > 0)(MapResult!(__lambda5, Result)),
> candidates are:
> /home/bahman/Programs/D/dmd-2.071.0/linux/bin64/../../src/phobos/std/algorithm/sorting.d(1027,1):
>        std.algorithm.sorting.sort(alias less = "a < b", SwapStrategy ss
> = SwapStrategy.unstable, Range)(Range r) if ((ss ==
> SwapStrategy.unstable && (hasSwappableElements!Range ||
> hasAssignableElements!Range) || ss != SwapStrategy.unstable &&
> hasAssignableElements!Range) && isRandomAccessRange!Range &&
> hasSlicing!Range && hasLength!Range)
> source/services.d(168,5): Error: var has no effect in expression (theRange)
> dmd failed with exit code 1.

Alright...further experiments.  The following works:

    sort!((pp1, pp2) => cmp(pp1.price,  pp2.price) > 0)(theRange)

So it may be something about what kind of range I'm passing to `sort`. Am I right?

-- 
Bahman

On 07/26/2016 10:11 AM, Bahman Movaqar wrote:
> Alright...further experiments.  The following works:
> 
>     sort!((pp1, pp2) => cmp(pp1.price,  pp2.price) > 0)(theRange)
> 
> So it may be something about what kind of range I'm passing to `sort`. Am I right?
> 

I meant

    sort!((pp1, pp2) => cmp(pp1.price,  pp2.price) > 0)(theRange.array)


-- 
Bahman

On Tuesday, July 26, 2016 10:11:43 Bahman Movaqar via Digitalmars-d-learn wrote:
> On 07/26/2016 09:35 AM, Bahman Movaqar wrote:
> > I have a range which is the result of a couple of chained range
> >
> > operations, and each element is:
> >     Tuple!(string, "product", double, "price")
> >
> > Now I'd like to sort the range by "price" using:
> >     sort!((pp1, pp2) => cmp(pp1.price,  pp2.price) > 0)(theRange)
> >
> > But I get a compile time error:
> >
> > source/services.d(166,63): Error: template std.algorithm.sorting.sort
> > cannot deduce function from argument types !((pp1, pp2) =>
> > cmp(pp1.price, pp2.price) > 0)(MapResult!(__lambda5, Result)),
> > candidates are:
> >
> > 
/home/bahman/Programs/D/dmd-2.071.0/linux/bin64/../../src/phobos/std/algorithm/sorting.d(1027,1):
> >        std.algorithm.sorting.sort(alias less = "a < b", SwapStrategy ss
> >
> > = SwapStrategy.unstable, Range)(Range r) if ((ss ==
> > SwapStrategy.unstable && (hasSwappableElements!Range ||
> > hasAssignableElements!Range) || ss != SwapStrategy.unstable &&
> > hasAssignableElements!Range) && isRandomAccessRange!Range &&
> > hasSlicing!Range && hasLength!Range)
> > source/services.d(168,5): Error: var has no effect in expression
> > (theRange)
> > dmd failed with exit code 1.
>
> Alright...further experiments.  The following works:
>
>     sort!((pp1, pp2) => cmp(pp1.price,  pp2.price) > 0)(theRange)
>
> So it may be something about what kind of range I'm passing to `sort`. Am I right?

sort requires a random access range. Without knowing exactly which algorithms your using, I can't say for sure that that's the problem, but usually it is. Most of the time, you don't end up with a random access range after chaining several range-based functions. You _can_, but it depends entirely on which functions they are and the type of your original range.

It's frequently the case that if you want to sort a range, you have to call array() on it to convert it to an array, and then you can sort the array.

- Jonathan M Davis

26.07.2016 09:11, Jonathan M Davis via Digitalmars-d-learn пишет:
>
> It's frequently the case that if you want to sort a range, you have to call
> array() on it to convert it to an array, and then you can sort the array.
>
> - Jonathan M Davis
>
Another option is `makeIndex` (std.algorithm.sorting) and then sorting of that index.

On 07/26/2016 10:41 AM, Jonathan M Davis via Digitalmars-d-learn wrote:
>> So it may be something about what kind of range I'm passing to `sort`. Am I right?
> 
> sort requires a random access range. Without knowing exactly which algorithms your using, I can't say for sure that that's the problem, but usually it is. Most of the time, you don't end up with a random access range after chaining several range-based functions. You _can_, but it depends entirely on which functions they are and the type of your original range.
> 
> It's frequently the case that if you want to sort a range, you have to call array() on it to convert it to an array, and then you can sort the array.

Thanks...that explains it.

-- 
Bahman

On 07/26/2016 11:42 AM, drug wrote:
> Another option is `makeIndex` (std.algorithm.sorting) and then sorting
> of that index.

That's an interesting option; at least I don't have to touch the range. Thanks.

-- 
Bahman