> On 30 Aug 2020, at 09:03, Jeff Allen <[email protected]> wrote:
>
> On 29/08/2020 14:17, Barry Scott wrote:
>>> On 29 Aug 2020, at 13:42, Filipp Bakanov <[email protected]
>>> <mailto:[email protected]>> 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
>>>
>>> <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
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