This seems to be true of any range function really... is there a way to access the key within my range?

Example of what I want to do:

auto x = [1,2,3,4,5];
x.filter( x_key % 2 == 1 ).sum(); // sum odd elements in array

On Tuesday, 9 February 2016 at 20:40:44 UTC, Charles wrote:
> This seems to be true of any range function really... is there a way to access the key within my range?
>
> Example of what I want to do:
>
> auto x = [1,2,3,4,5];
> x.filter( x_key % 2 == 1 ).sum(); // sum odd elements in array

x.filter!(x_key => x_key % 2 == 1).sum();

On 2/9/16 3:40 PM, Charles wrote:
> This seems to be true of any range function really... is there a way to
> access the key within my range?
>
> Example of what I want to do:
>
> auto x = [1,2,3,4,5];
> x.filter( x_key % 2 == 1 ).sum(); // sum odd elements in array

An array is not an indexed range. It only works with foreach by key because of special foreach behavior.

What you want is std.range.enumerate:

import std.range;
import std.algorithm;
import std.stdio;

void main()
{
    auto x = [1, 2, 3, 4, 5];
    writeln(x.enumerate.filter!(a => a[0] % 2 == 1).map!(a => a[1]).sum); // 6
}

-Steve

On Tuesday, 9 February 2016 at 20:44:34 UTC, cym13 wrote:
> On Tuesday, 9 February 2016 at 20:40:44 UTC, Charles wrote:
>> This seems to be true of any range function really... is there a way to access the key within my range?
>>
>> Example of what I want to do:
>>
>> auto x = [1,2,3,4,5];
>> x.filter( x_key % 2 == 1 ).sum(); // sum odd elements in array
>
> x.filter!(x_key => x_key % 2 == 1).sum();

Oh man, I really messed up my example, and did a poor one at that.

Better example:

auto x = [2,4,6,8,10];
x.filter( x_key => x_key % 2 == 1 ).sum(); // sums 2 + 6 + 10 == 18

On Tuesday, 9 February 2016 at 20:48:01 UTC, Steven Schveighoffer wrote:
> On 2/9/16 3:40 PM, Charles wrote:
>> This seems to be true of any range function really... is there a way to
>> access the key within my range?
>>
>> Example of what I want to do:
>>
>> auto x = [1,2,3,4,5];
>> x.filter( x_key % 2 == 1 ).sum(); // sum odd elements in array
>
> An array is not an indexed range. It only works with foreach by key because of special foreach behavior.
>
> What you want is std.range.enumerate


Exactly! Thanks!

Interestingly, hackerrank doesn't seem to have it. They're using 2.067.0-b1 on Ubuntu 14.04.

On 02/09/2016 12:54 PM, Charles wrote:
> On Tuesday, 9 February 2016 at 20:48:01 UTC, Steven Schveighoffer wrote:
>> On 2/9/16 3:40 PM, Charles wrote:
>>> This seems to be true of any range function really... is there a way to
>>> access the key within my range?
>>>
>>> Example of what I want to do:
>>>
>>> auto x = [1,2,3,4,5];
>>> x.filter( x_key % 2 == 1 ).sum(); // sum odd elements in array
>>
>> An array is not an indexed range. It only works with foreach by key
>> because of special foreach behavior.
>>
>> What you want is std.range.enumerate
>
>
> Exactly! Thanks!
>
> Interestingly, hackerrank doesn't seem to have it. They're using
> 2.067.0-b1 on Ubuntu 14.04.
>

For this specific problem, you can combine drop() and stride() (and even sum()! ;) ):

import std.range;
import std.algorithm;
import std.stdio;

void main()
{
    auto x = [1, 2, 3, 4, 5];
    writeln(x.drop(1).stride(2).sum); // 6
}

Ali