> On 30 Aug 2020, at 12:25, Filipp Bakanov <fil...@bakanov.su> wrote: > > > It's expected that python single iterating would be slower than two times C > iterating. Nevertheless one time C iterating will be probably faster than a > separate min + index. > > >> I think one would want argmin() and argmax() to work with general iterables > How is it supposed to work with set or dict or other iterables without clear > order? > > My last case was to find the min index of the array part. index_min could > accept the starting element index, as index does. > > a = [1, 4, 1, 2, 3] > print(a.index_min()) # 0 > print(a.index_min(1)) # 2
Of course this could be implemented in C in python, but you are going to have to convince the python developers that it’s important enough to want to maintain the code. Is your use of such a function so performance sensitive that you need this in C? Have you considered writing this as a C extension for your own use? Barry > > > > On Sun, 30 Aug 2020 at 11:52, Barry Scott <ba...@barrys-emacs.org> wrote: >> >> >>>> On 30 Aug 2020, at 09:03, Jeff Allen <ja...@farowl.co.uk> wrote: >>>> >>>> On 29/08/2020 14:17, Barry Scott wrote: >>>>>> On 29 Aug 2020, at 13:42, Filipp Bakanov <fil...@bakanov.su> wrote: >>>>>> >>>>>> I'd like to propose adding argmax and argmin functions to the python >>>>>> list. These functions return the index of a maximum / minimum element of >>>>>> the list. Eg: >>>>>> >>>>>> a = [1, 4, 2, 3] >>>>>> print(a.argmax()) # 1 >>>>>> print(a.argmin()) # 0 >>>>>> >>>>>> It's a very popular request (based on stackoverflow >>>>>> https://stackoverflow.com/questions/16945518/finding-the-index-of-the-value-which-is-the-min-or-max-in-python >>>>>> ), and currently there is no elegant way to find it. >>>>>> >>>>>> What do you think? >>>>> >>>>> Just do this: >>>>> >>>>> >>> a=[1,4,2,3] >>>>> >>> min(a) >>>>> 1 >>>>> >>> a.index(min(a)) >>>>> 0 >>>>> >>> a.index(max(a)) >>>>> 1 >>>>> >>>>> Barry >>>>> >>>> This has the drawback of passing twice over the list. The following >>>> doesn't, but the complexity somewhat makes Filipp's point: >>>> >>>> >>> min((e, i) for i, e in enumerate(a))[1] >>>> 0 >>>> >>> That is 4x slower then my code for 1,000,000 items. >>> >>> --------------- a.py -------------- >>> import sys >>> import time >>> import random >>> >>> alg = sys.argv[1] >>> size = int(sys.argv[2]) >>> >>> x = [random.randint(0, 1_000_000) for _ in range(size)] >>> >>> start = time.time() >>> >>> if alg == 'barry': >>> >>> m = x.index(min(x)) >>> >>> elif alg == 'jeff': >>> >>> m = min((e, i) for i, e in enumerate(x))[1] >>> >>> end = time.time() >>> >>> print( alg, end-start, (end-start)/size ) >>> ------------------------- >>> >>> Here is the output I got on my laptop. >>> >>> barry 0.022754907608032227 2.2754907608032226e-08 >>> barry 0.03325295448303223 3.325295448303223e-08 >>> barry 0.034243106842041016 3.4243106842041016e-08 >>> barry 0.02784109115600586 2.784109115600586e-08 >>> jeff 0.13722586631774902 1.3722586631774904e-07 >>> jeff 0.1359708309173584 1.359708309173584e-07 >>> jeff 0.13658690452575684 1.3658690452575684e-07 >>> >>> I think one would want argmin() and argmax() to work with general >>> iterables, so I wonder if the stdlib would not be a better home than list >>> itself. I half expected it to be an itertools recipe. The advantage of a >>> recipe is that variations such as needing the last occurrence of the >>> minimum are easily accommodated. >>> >> >> Surely its index_min() and index_max() not argmin() and argmax(). >> >> Barry >> >> _______________________________________________ >> Python-ideas mailing list -- python-ideas@python.org >> To unsubscribe send an email to python-ideas-le...@python.org >> https://mail.python.org/mailman3/lists/python-ideas.python.org/ >> Message archived at >> https://mail.python.org/archives/list/python-ideas@python.org/message/VMSSYHAOST7K3WNHO3JOQENI6G5CXZZ5/ >> Code of Conduct: http://python.org/psf/codeofconduct/
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