Premise: Write a program that counts the frequencies of each word in a text, and output each word with its count and line numbers where it appears. We define a word as a contiguous sequence of non-white-space characters. Different capitalizations of the same character sequence should be considered same word (e.g. Python and python). The output is formatted as follows: each line begins with a number indicating the frequency of the word, a white space, then the word itself, and a list of line numbers containing this word. You should output from the most frequent word to the least frequent. In case two words have the same frequency, the lexicographically smaller one comes first. All words are in lower case in the output.
# Amazing Python libraries that prevent re-invention of wheels. import re import collections import string from operator import itemgetter # Simulate work for terminal print 'Scanning input for word frequency...' # Text files input = open('input.txt', 'r') output = open('output.txt', 'w') # Reads every word in input as lowercase while ignoring punctuation and # returns a list containing 2-tuples of (word, frequency). list = collections.Counter(input.read().lower() .translate(None, string.punctuation).split()).most_common() # Sorts the list by frequency in descending order. list = sorted(list, key=itemgetter(0)) # Sorts the list by lexicogrpahical order in descending order while maintaining # previous sorting. list = sorted(list, key=itemgetter(1), reverse=True) # Gets the lines where each word in list appears in the input. for word in list: lineList =  # Reads the input line by line. Stores each text line in 'line' and keeps a # counter in 'lineNum' that starts at 1. for lineNum, line in enumerate(open('input.txt'),1): # If the word is in the current line then add it to the list of lines # in which the current word appears in. The word frequency list is not # mutated. This is stored in a separate list. if re.search(r'(^|\s)'+word+'\s', line.lower().translate(None, string.punctuation), flags=re.IGNORECASE): lineList.append(lineNum) # Write output with proper format. output.write(str(word) + ' ' + word + ' ' + str(lineList)+'\n') # End work simulation for terminal print 'Done! Output in: output.txt'
How can I get the line numbers without re-reading the text? I want to achieve sub-O(n^2) time complexity. I am new to Python so feedback on other aspects is greatly appreciated as well.