collections in python code example

Example 1: Python Ordered Dictionary

from collections import OrderedDict

# Remembers the order the keys are added!
x = OrderedDict(a=1, b=2, c=3)

Example 2: python counter

>>> # Tally occurrences of words in a list
>>> cnt = Counter()
>>> for word in ['red', 'blue', 'red', 'green', 'blue', 'blue']:
...     cnt[word] += 1
>>> cnt
Counter({'blue': 3, 'red': 2, 'green': 1})

>>> # Find the ten most common words in Hamlet
>>> import re
>>> words = re.findall(r'\w+', open('hamlet.txt').read().lower())
>>> Counter(words).most_common(10)
[('the', 1143), ('and', 966), ('to', 762), ('of', 669), ('i', 631),
 ('you', 554),  ('a', 546), ('my', 514), ('hamlet', 471), ('in', 451)]

Example 3: python collections to dictionary

list = ["a","c","c","a","b","a","a","b","c"]
cnt = Counter(list)
od = OrderedDict(cnt.most_common())
for key, value in od.items():
    print(key, value)

Example 4: python collections

# Dictionary where key values default to a list:
	a = collections.defaultdict(list)   
# Dictionary where key values default to 0:
	a = collections.defaultdict(int)
# Dictionary where key values default to another dictionary:
	a = collections.defaultdict(dict)

'''
Example:
  In a regular dictionary, if you did the following:
  
    a = {}
    if a['apple'] == 1:
        return True    
    else:
        return False
        
  You'd get an error, because 'apple' does not exist in dictionary. 
  However, if you use collections:
    
    a = collections.defaultdict(int)
    if a['apple'] == 1:
		return True
    else:
        return False
    
  This would not give an error, and False would be returned.
  Also, the dictionary would now have the key 'apple' with a
  default integer value of 0 inside it.
  
  If you used say, collections.defaultdict(list), the default value
  would be an empty list instead of 0.
  
'''

Example 5: python collections

list = [1,2,3,4,1,2,6,7,3,8,1]
Counter(list)