Oh, ops, sorry my fault, I understood the question reversed :D I think that if we had a compute function that returns indices of a matching value that could also be applied to masks to retrieve the indices of any "true" value thus also solving your question if combined with is_in (or any other predicate at that point). That might be a reasonable addition to compute functions.
On Sun, Nov 28, 2021 at 7:00 AM Niranda Perera <[email protected]> wrote: > Hi guys, sorry for the late reply. > > Yes, Joris is right. I want the converse (I think 😊 ) of index in. I was > discussing this with Eduardo in zulip [1]. > > I was hoping that I could do this. > ``` > values = pa.array([1, 2, 2, 3, 4, 1]) > to_find= pa.array([1, 2, 1]) > indices = pc.index_in(to_find, value_set=values) # expected = [0, 5, 1, > 2, 0, 5] received = [0, 1, 0] > ``` > So, index_in does not handle duplicated indices of values (I am guessing > it creates a hashmap of values, and not a multimap). > > One suggestion was to use `aggregations.index`. And I think that might > work recursively, as follows. But I haven't tested this. > ``` > indices = [] > for f in to_find: > idx = -1 > while true: > idx = pc.index(values, f, start=idx + 1, end=len(values)) > if idx == -1: > break > else: > indices.append(idx) > ``` > > But I was thinking if it would make sense to give a method to find all > indices of a value (inner while loop)? > > Best > > [1] > https://ursalabs.zulipchat.com/#narrow/stream/180245-dev/topic/Find.20a.20value.20indices.20in.20an.20array/near/262351923 > > > On Thu, Nov 25, 2021 at 3:14 PM Joris Van den Bossche < > [email protected]> wrote: > >> I think "index_in" does the index in the other way around? It gives, >> for each value of the array, the index in the set. While if I >> understand the question correctly, Niranda is looking for the index >> into the array for elements that are present in the set. >> >> Something like that could be achieved by using "is_in", and then >> getting the indices of the True values: >> >> >>> pc.is_in(pa.array([1, 2, 3]), value_set=pa.array([1, 3])) >> <pyarrow.lib.BooleanArray object at 0x7fcc96896a00> >> [ >> true, >> false, >> true >> ] >> >> To get the location of the True values, in numpy this is called >> "nonzero", and we have an open JIRA for adding this as a kernel >> (https://issues.apache.org/jira/browse/ARROW-13035) >> >> On Thu, 25 Nov 2021 at 11:17, Alessandro Molina >> <[email protected]> wrote: >> > >> > I think index_in is what you are looking for >> > >> > >>> pc.index_in(pa.array([1, 2, 3]), value_set=pa.array([1, 3])) >> > <pyarrow.lib.Int32Array object at 0x11e2a6580> >> > [ >> > 0, >> > null, >> > 1 >> > ] >> > >> > On Sat, Nov 20, 2021 at 4:49 AM Niranda Perera < >> [email protected]> wrote: >> >> >> >> Hi all, is there a compute API for searching a value index (and a set >> of values) in an Array? >> >> ex: >> >> ```python >> >> a = [1, 2, 2, 3, 4, 1] >> >> values= pa.array([1, 2, 1]) >> >> >> >> index = find_index(a, 1) # = [0, 5] >> >> indices = find_indices(a, values) # = [0, 1, 2, 5] >> >> ``` >> >> I am currently using `compute.is_in` and traversing the true indices >> of the result Bitmap. Is there a better way? >> >> >> >> Best >> >> -- >> >> Niranda Perera >> >> https://niranda.dev/ >> >> @n1r44 >> >> >> > > > -- > Niranda Perera > https://niranda.dev/ > @n1r44 <https://twitter.com/N1R44> > >
