[Tutor] custom comparator with ordered list

[Anish Kumar]

> anish singh wrote:
> 
>> I need a custom comparator.
>> 
>> dictionary = {a:[b,c], d:[e,f]}
>> 
>> If both 'b' and 'e' belong to the same bin
>> then it should be compared based on 'c' and 'f'.
>> 
>> However, I want to also represent the result of the
>> sorted operation in a ordered dictionary as order is
>> important.
>> 
>> My custom comparator is something like this:
>> 
>> 
>> ''' x and y is a list of two elements each'''
>> def cmpr(x, y):
>>    r = 3
>>    if x[0]//r != y[0]//r:
>>        return x[0]//r < y[0]//r
>>    return x[1] < y[1]
> 
> This looks like it should be called less() rather than compare() as it 
> doesn't differentiate between the x < y and x == y case.
> 
>> Please note it is not exactly comparing the first elements
>> of the value but checking if they belong to the same bin
>> and they do then it checks the second element as as shown
>> above.
> 
> The effect should be the same.

Well no, take the case of [1,100] and [2,0]
Both belong to same bin suppose then it should
be sorted based on second index and I would 
expect [2,0] [1,100] as output.
This is not happening currently with the original
code I have sent.

> 
>> Example:
>> {0:[0, 8], 1:[2, 5], 2:[2, 11], 3:[16, 17], 4:[13, 14], 5:[1, 17], 6:[17,
>> 17] }
>> output should be:
>> {1:[2, 5], 0:[0, 8], 2:[2, 11], 5:[1, 17], 4:[13, 14], 3:[16, 17], 6:[17,
>> 17] }
> 
>>>> input = {0:[0, 8], 1:[2, 5], 2:[2, 11], 3:[16, 17], 4:[13, 14], 5:[1, 
> 17], 6:[17,
> ... 17] }
>>>> wanted = {1:[2, 5], 0:[0, 8], 2:[2, 11], 5:[1, 17], 4:[13, 14], 3:[16, 
> 17], 6:[17,
> ... 17] }
>>>> output = {k: v for k, v in sorted(input.items(), key=lambda x: (x[1]
> [0]//3, x[1][1]))}
>>>> assert list(output.items()) == list(wanted.items())
> 
> As written it will work with CPython 3.6. However, for compatibility with 
> other versions of Python I recommend that you replace the plain dicts above 
> with collections.OrderedDict instances. Quoting
> 
> https://docs.python.org/dev/whatsnew/3.6.html#whatsnew36-pep520
> 
> """
> The order-preserving aspect of this new [dict] implementation is considered 
> an implementation detail and should not be relied upon [...]
> """
> 
> 
> 
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