How to find most common elements of a list?
In Python 2.7 and above there is a class called Counter which can help you:
from collections import Counter
words_to_count = (word for word in word_list if word[:1].isupper())
c = Counter(words_to_count)
print c.most_common(3)
Result:
[('Jellicle', 6), ('Cats', 5), ('And', 2)]
I am quite new to programming so please try and do it in the most barebones fashion.
You could instead do this using a dictionary with the key being a word and the value being the count for that word. First iterate over the words adding them to the dictionary if they are not present, or else increasing the count for the word if it is present. Then to find the top three you can either use a simple O(n*log(n)) sorting algorithm and take the first three elements from the result, or you can use a O(n) algorithm that scans the list once remembering only the top three elements.
An important observation for beginners is that by using builtin classes that are designed for the purpose you can save yourself a lot of work and/or get better performance. It is good to be familiar with the standard library and the features it offers.
Is't it just this ....
word_list=['Jellicle', 'Cats', 'are', 'black', 'and', 'white,', 'Jellicle', 'Cats',
'are', 'rather', 'small;', 'Jellicle', 'Cats', 'are', 'merry', 'and',
'bright,', 'And', 'pleasant', 'to', 'hear', 'when', 'they', 'caterwaul.',
'Jellicle', 'Cats', 'have', 'cheerful', 'faces,', 'Jellicle', 'Cats',
'have', 'bright', 'black', 'eyes;', 'They', 'like', 'to', 'practise',
'their', 'airs', 'and', 'graces', 'And', 'wait', 'for', 'the', 'Jellicle',
'Moon', 'to', 'rise.', '']
from collections import Counter
c = Counter(word_list)
c.most_common(3)
Which should output
[('Jellicle', 6), ('Cats', 5), ('are', 3)]
If you are using an earlier version of Python or you have a very good reason to roll your own word counter (I'd like to hear it!), you could try the following approach using a dict.
Python 2.6.1 (r261:67515, Feb 11 2010, 00:51:29)
[GCC 4.2.1 (Apple Inc. build 5646)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> word_list = ['Jellicle', 'Cats', 'are', 'black', 'and', 'white,', 'Jellicle', 'Cats', 'are', 'rather', 'small;', 'Jellicle', 'Cats', 'are', 'merry', 'and', 'bright,', 'And', 'pleasant', 'to', 'hear', 'when', 'they', 'caterwaul.', 'Jellicle', 'Cats', 'have', 'cheerful', 'faces,', 'Jellicle', 'Cats', 'have', 'bright', 'black', 'eyes;', 'They', 'like', 'to', 'practise', 'their', 'airs', 'and', 'graces', 'And', 'wait', 'for', 'the', 'Jellicle', 'Moon', 'to', 'rise.', '']
>>> word_counter = {}
>>> for word in word_list:
... if word in word_counter:
... word_counter[word] += 1
... else:
... word_counter[word] = 1
...
>>> popular_words = sorted(word_counter, key = word_counter.get, reverse = True)
>>>
>>> top_3 = popular_words[:3]
>>>
>>> top_3
['Jellicle', 'Cats', 'and']
Top Tip: The interactive Python interpretor is your friend whenever you want to play with an algorithm like this. Just type it in and watch it go, inspecting elements along the way.
To just return a list containing the most common words:
from collections import Counter
words=["i", "love", "you", "i", "you", "a", "are", "you", "you", "fine", "green"]
most_common_words= [word for word, word_count in Counter(words).most_common(3)]
print most_common_words
this prints:
['you', 'i', 'a']
the 3 in "most_common(3)", specifies the number of items to print.
Counter(words).most_common() returns a a list of tuples with each tuple having the word as the first member and the frequency as the second member.The tuples are ordered by the frequency of the word.
`most_common = [item for item in Counter(words).most_common()]
print(str(most_common))
[('you', 4), ('i', 2), ('a', 1), ('are', 1), ('green', 1), ('love',1), ('fine', 1)]`
"the word for word, word_counter in", extracts only the first member of the tuple.