double sorting. first by index, then by count uncategorized solution for Sort Array by Element Frequency by kaisa.kucherenko - python coding challenges

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double sorting. first by index, then by count solution in Uncategorized category for Sort Array by Element Frequency by kaisa.kucherenko

def frequency_sort(items):
    """ First sort by list.index() using lambda. 
        Then, once again, we sort already by list.count(), also using lambda
        The first sorting by index is needed for the case when there are 
        several elements with the same list.count()
    """
    return sorted(sorted(items, key=lambda item: items.index(item)), key=lambda item: items.count(item), reverse=True)

May 27, 2020

Comments:

vvm70 on May 29, 2020, 10:44 a.m.
It can be written without lambda: <pre class='brush: python'>key=items.index </pre> because type of both lambda and index is a function. You can find out this with the type() function

shobble on June 3, 2020, 1:19 a.m.
You can avoid the double sort entirely by having the key function return a tuple of `(freq, pos)` to break ties where they have the same frequency. Tuples sort element-wise, so it will only look at later elements if the first ones are the same. <pre class='brush: python'>def frequency_sort2(items): return sorted(items, key=lambda item: (-items.count(item), items.index(item))) </pre> Shows the idea, note the `-` to sort higher frequencies first, since `-10` sorts before `-2`, etc.

List, list and list again

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