for 循环、dict.setdefault(key,[]).append(value)、result=defaultdict(list)

Using a variety of data processing for loop

In [24]:

words =['apple','pare','banana','and','peach']

 

 

In [57]:

byletter = {}

for word in words:

    letter=word[0]

    if letter  in byletter:

        byletter[letter].append(word)

    else:

        byletter[letter]=[word]

 

In [58]:

byletter

 

 

Out[58]:

{'a': ['apple', 'and'], 'p': ['pare', 'peach'], 'b': ['banana']}

 

dict.setdefault(key,[]).append(value)

setdefault dictionary object is an instance method, the receiving two parameters, and similar usage dictionary get method, but more powerful than get. It can be set to a default value for the dictionary key (if the key is not in the dictionary of the time) to set default values ​​get method does not change the original dictionary, and the default value setdefault setting will change the value of the original dictionary.

In [41]:

by_letters={}

for word in words:

    letter=word[0]

    by_letters.setdefault(letter,[]).append(word)

 

 

In [43]:

  by_letters

 

 

Out[43]:

{'a': ['apple', 'and'], 'p': ['pare', 'peach'], 'b': ['banana']}

In [59]:

 

data=[('p',1),('p',2),('p',3),('h',4),('h',5),('h',6)]

 

result=defaultdict(list)

defaultdict a plant belonging to the function of the collections module for building an object dictionary, a receiving function (callable) object as a parameter. What type parameter returns, key value that corresponds to what type.

In [66]:

  from collections import defaultdict

results=defaultdict(list)

data=[('p',1),('p',2),('p',3),('h',4),('h',5),('h',6)]

for (key,value) in data:

    results[key].append(value)

 

 

In [67]:

results

 

 

Out[67]:

defaultdict(list, {'p': [1, 2, 3], 'h': [4, 5, 6]})