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July 30, 2012
Has AA .keys the same order as .values?
Hi,

I need to interleave multiple arrays stored in an AA into a 
single array, and the keys of the AA need to be stored separately 
in the same order as the interleaved data. As an example:

auto aa = [
  "1" : [1, 2],
  "2" : [3, 4],
  "3" : [5, 6],
  "4" : [7, 8]
]

auto values = aa.values;
auto keys =  aa.keys;

//Store keys, and interleave values

I did a quick test and values has the same order as keys, but is 
this guaranteed to be the case?
July 30, 2012
Re: Has AA .keys the same order as .values?
On 30-07-2012 18:00, Rene Zwanenburg wrote:
> Hi,
>
> I need to interleave multiple arrays stored in an AA into a single
> array, and the keys of the AA need to be stored separately in the same
> order as the interleaved data. As an example:
>
> auto aa = [
>    "1" : [1, 2],
>    "2" : [3, 4],
>    "3" : [5, 6],
>    "4" : [7, 8]
> ]
>
> auto values = aa.values;
> auto keys =  aa.keys;
>
> //Store keys, and interleave values
>
> I did a quick test and values has the same order as keys, but is this
> guaranteed to be the case?

Ordering is not guaranteed at all in AAs.

-- 
Alex Rønne Petersen
alex@lycus.org
http://lycus.org
July 30, 2012
Re: Has AA .keys the same order as .values?
Rene Zwanenburg:

> I did a quick test and values has the same order as keys, but 
> is this guaranteed to be the case?

In Python they they are guaranteed to have the same order (if you 
don't modify the associative array in the loops).

In D the current implementation gives them in the same order 
(again if you don't modify the associative array in the 
meantime), because this is the most natural way to implement the 
algorithm. But as far as I know there is no guarantee this is 
always true.

To solve this problem I have suggested to introduce another AA 
pseudomethod, named byPair, that returns a lazy range of 
key-value tuples, similar to the dict.iteritems() method of 
Python2:

http://d.puremagic.com/issues/show_bug.cgi?id=5466

But Andrei has not introduced this enhancement because it 
requires to import the std.typecons module from the object.d, 
tying it even more to Phobos.

Until a solution like byPair is introduced, I think the D docs 
should be updated, to state that the byKey and byValue yield 
corresponding keys-values.

---------------------

Alex Rønne Petersen:

> Ordering is not guaranteed at all in AAs.

This is a different thing.

Bye,
bearophile
July 30, 2012
Re: Has AA .keys the same order as .values?
> Ordering is not guaranteed at all in AAs.

I don't want .keys and .values to have the same order as the 
order in which it was filled, I understand this is impossible. 
What I'd like is to have aa.values[i] == aa[aa.keys[i]]. I think 
this is easy to guarantee with typical AA implementations.
July 30, 2012
Re: Has AA .keys the same order as .values?
On Monday, 30 July 2012 at 16:21:17 UTC, bearophile wrote:
> Rene Zwanenburg:
>
>> I did a quick test and values has the same order as keys, but 
>> is this guaranteed to be the case?
>
> In Python they they are guaranteed to have the same order (if 
> you don't modify the associative array in the loops).
>
> In D the current implementation gives them in the same order 
> (again if you don't modify the associative array in the 
> meantime), because this is the most natural way to implement 
> the algorithm. But as far as I know there is no guarantee this 
> is always true.
>
> To solve this problem I have suggested to introduce another AA 
> pseudomethod, named byPair, that returns a lazy range of 
> key-value tuples, similar to the dict.iteritems() method of 
> Python2:
>
> http://d.puremagic.com/issues/show_bug.cgi?id=5466
>
> But Andrei has not introduced this enhancement because it 
> requires to import the std.typecons module from the object.d, 
> tying it even more to Phobos.
>
> Until a solution like byPair is introduced, I think the D docs 
> should be updated, to state that the byKey and byValue yield 
> corresponding keys-values.
>
> ---------------------
>
> Alex Rønne Petersen:
>
>> Ordering is not guaranteed at all in AAs.
>
> This is a different thing.
>
> Bye,
> bearophile

Great, thanks.
July 30, 2012
Re: Has AA .keys the same order as .values?
Rene Zwanenburg:

> Great, thanks.

See:
http://d.puremagic.com/issues/show_bug.cgi?id=8473
http://forum.dlang.org/thread/wztazusqjoispivajifh@forum.dlang.org

Bye,
bearophile
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