[Numpy-discussion] Would it be possible to enhance np.unique(.) with a keyword kind

[josef.pktd at gmail.com]

On Mon, Dec 19, 2011 at 8:16 PM, eat <e.antero.tammi at gmail.com> wrote:
> Hi,
>
> On Tue, Dec 20, 2011 at 2:33 AM, <josef.pktd at gmail.com> wrote:
>>
>> On Mon, Dec 19, 2011 at 6:27 PM, eat <e.antero.tammi at gmail.com> wrote:
>> > Hi,
>> >
>> > Especially when the keyword return_index of np.unique(.) is specified to
>> > be
>> > True, would it in general also be reasonable to be able to specify the
>> > sorting algorithm of the underlying np.argsort(.)?
>> >
>> > The rationale is that (for at least some of my cases) higher level
>> > algorithms seems to be too over complicated unless I'm not able to
>> > request a
>> > stable sorting order from np.unique(.) (like np.unique(., return_index=
>> > True, kind= 'mergesort').
>> >
>> > (FWIW, I apparently do have a working local hack for this kind of
>> > functionality, but without extensive testing of 'all' corner cases).
>>
>> Just to understand this:
>>
>> Is the return_index currently always the first occurrence or random?
>
> No, for current implementation it's not always the first occurrence
> returned. AFAIK, the only stable algorithm to provide this is ' mergesort'
> and that's why I'll like to have a keyword 'kind' to propagate down to then
> internals.

Thanks, then I'm all in favor of mergesort.

>>
>>
>> I haven't found a use for return_index yet (but use return_inverse a
>> lot), but if we are guaranteed to get the first instance, then this
>> could be very useful.
>
> I think that 'return_inverse' will suffer of the same
> nondeterministic behavior as well.

I don't think so, because there is a unique mapping from observations
to unique items.

Josef

>
> Thanks,
> eat
>>
>>
>> Josef
>>
>>
>> >
>> >
>> > Thanks,
>> > eat
>> >
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