Huffman code use case.


Huffman code is a special type of optimal prefix code that is widely used for lossless data compression in information theory and computer science. An algorithm was elaborated by MIT student David A. Huffman. The implementation idea is to set variable-length codes to input characters, lengths of the assigned codes are based on the frequencies of corresponding input characters. In the end the most frequent character obtains the smallest code and the least frequent character receives the largest code.

Huffman Coding algorithm.



As in other entropy encoding methods, more common symbols are generally represented using fewer bits than less common symbols. In practice Huffman Coding is generally useful to compress the data in which there are frequently occurring characters. A great use case of Huffman coding is conventional data compression formats like ZIP.


Huffman Coding Python code:



from heapq import heappush, heappop, heapify
from collections import defaultdict
import collections

txt = "BCAADDDCCACACAC BCAADDDCCACACAC"

symb2freq = collections.Counter(txt) #counts letter frequency and puts in dictionary

def encode(symb2freq):

    heap = [[freq, [symbol, ""]] for symbol, freq in symb2freq.items()] #converts dictionary to a list in order to sort out alphabets in terms of frequencies

    heapify(heap) #Sorting out the list so that 1st element is always the smallest

    while len(heap) > 1:#while there is more than 1 element in the list

        left = heappop(heap) #Takes the lowest frequency from the list

        # print("lo=", left)

        right = heappop(heap) #Takes the lowest frequency from the list        

        for x in left[1:]:
            x[1] = '0' + x[1]
        for x in right[1:]:
            x[1] = '1' + x[1]
        add_freq= [left[0] + right[0]] + left[1:] + right[1:] #adds the frequencies and inserts frequency, symbol and alphabet (0 or 1) into one list

        heappush(heap, add_freq )#inserts add_freq into heap

    return sorted(heappop(heap)[1:], key=lambda p: (len(p[-1]), p))

huff = encode(symb2freq)
print ("Symbol\tWeight\tCode")
for p in huff:
    print ("%s\t%s\t%s" % (p[0], symb2freq[p[0]], p[1]))

Huffman code




See also related topics: