Python custom comparator to sort a specific list

Question

I have an input list like [1,2,2,1,6] the task in hand is to sort by the frequency. I have solved this question and am getting the output as [1,2,6]. But the caveat is that if two of the numbers have the same count like count(1) == count(2). So the desired output is [2,1,6] then in the output array, 2 must come before 1 as 2 > 1.

So for the input [1,1,2,2,3,3] the output should be [3,2,1]. The counts are the same so they got sorted by their actual values.

This is what I did

input format:

number of Test cases
The list input.

def fun(l):
    d = {}
    for i in l:
        if i in d:
            d[i] += 1 
        else:
            d[i] = 1 
    d1 = sorted(d,key = lambda k: d[k], reverse=True)

    return d1
try:
    test = int(input())
    ans = []
    while test:
        l = [int(x) for x in input().split()]
        ans.append(fun(l))
        test -= 1
    for i in ans:
        for j in i:

            print(j, end = " ")
        print()    
except:
    pass

Jorge Avila · Accepted Answer · 2020-03-31 04:48:47Z

2

I think that this can help you. I added reverse parameter that is setting by default to True, because that gives the solution, but I wrote in the code where you can edit this as you may.

Here is the code:

from collections import defaultdict # To use a dictionary, but initialized with a default value

def fun(l, reverse = True):
    d = defaultdict(int)    
    # Add count
    for i in l:
        d[i] += 1 

    # Create a dictionary where keys are values
    new_d = defaultdict(list)
    for key,value in d.items(): 
        new_d[value].append(key)

    # Get frequencies
    list_freq = list(new_d.keys())
    list_freq.sort(reverse = reverse) #YOU CAN CHANGE THIS
    list_freq

    # Add numbers in decreasing order by frequency
    # If two integers have the same frequency, the greater number goes first
    ordered_list = []
    for number in list_freq:
        values_number = new_d[number]
        values_number.sort(reverse = reverse) # YOU CAN CHANGE THIS
        ordered_list.extend(values_number)

    return ordered_list

Examples:

l = [1,2,2,1,6]
fun(l)
#Output [2,1,6]

I hope this can help you!

edited Mar 31, 2020 at 4:48

answered Mar 31, 2020 at 4:24

Jorge Avila

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2 Comments

Jorge Avila Over a year ago

In this case, i will take another approach, not to use your exactly function fun

Subham Banerjee Over a year ago

can you explain a bit why we have to pass reverse = False

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