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digitalmars.D.learn - Trouble using 'sort'

reply Bahman Movaqar <Bahma BahmanM.com> writes:
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
Jul 25 2016
parent reply Bahman Movaqar <Bahma BahmanM.com> writes:
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
Jul 25 2016
next sibling parent Bahman Movaqar <Bahma BahmanM.com> writes:
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
Jul 25 2016
prev sibling parent reply Jonathan M Davis via Digitalmars-d-learn writes:
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
Jul 25 2016
next sibling parent reply drug <drug2004 bk.ru> writes:
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.
Jul 26 2016
parent Bahman Movaqar <Bahma BahmanM.com> writes:
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
Jul 26 2016
prev sibling parent Bahman Movaqar <Bahma BahmanM.com> writes:
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
Jul 26 2016