user434180 user434180 - 8 days ago 3
Python Question

How to find most common elements of a list?

Given the following 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.', '']


I am trying to count how many times each word appears and display the top 3.

However I am only looking to find the top three that have the first letter capitalized and ignore all words that do not have the first letter capitalized.

I am sure there is a better way than this, but my idea was to do the following:


  1. put the first word in the list into another list called uniquewords

  2. delete the first word and all its duplicated from the original list

  3. add the new first word into unique words

  4. delete the first word and all its duplicated from original list.

  5. etc...

  6. until the original list is empty....

  7. count how many times each word in uniquewords appears in the original list

  8. find top 3 and print


Answer

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.