python列表计数元素

Question

I have a code as below

How can I find that abc is a list made up of lists?

Whats wrong with my map function?

I want my function to return count of each element in my input list divided by length of my list.

Something like

{'brown': 0.16666666666666666, 'lazy': 0.16666666666666666, 'jumps': 0.16666666666666666, 'fox': 0.16666666666666666,  'dog': 0.16666666666666666, 'quick': 0.16666666666666666}

My code:

quickbrownfox1=['quick', 'brown', 'fox', 'jumps', 'lazy', 'dog']
print quickbrownfox1


def tf(tokens):

    abc=([[x,(tokens.count(x))] for x in set(tokens)])
    print type(abc)#how to know that abc is made up of lists
    print type(abc[1])
    answer=abc.map(lambda input:(input(0)),input(1)/len(tokens)))

    return answer
    #return <FILL IN>

print tf((quickbrownfox1)) # Should give { 'quick': 0.1666 ... }
#print tf(tokenize(quickbrownfox)) # Should give { 'quick': 0.1666 ... }

_______________________________________

update 1

I updated my code as below. I get result [('brown', 0), ('lazy', 0), ('jumps', 0), ('fox', 0), ('dog', 0), ('quick', 0)] any idea why? If i do return return list(map(lambda input: (input[0], input[1]), abc)) , it gives correct result - [('brown', 1), ('lazy', 1), ('jumps', 1), ('fox', 1), ('dog', 1), ('quick', 1)]

from __future__ import division
quickbrownfox1=['quick', 'brown', 'fox', 'jumps', 'lazy', 'dog']

def islistoflists(i):
    if isinstance(i, list):
        if len(i) > 0 and all(isinstance(t, list) for t in i):
            return True
    return False


def tf(tokens):

    print(islistoflists(tokens))

    abc = ([[x,tokens.count(x)] for x in set(tokens)])
    return list(map(lambda input: (input[0], input[1] / len(tokens)), abc))

print tf(quickbrownfox1)

---

update 2

I am using pyspark/spark. Could that be a reason for issues that i am facing in update1?

Answer 1

The counter solution will definitely be better. Your use of tokens.count gives the code quadratic time complexity. Heres your code fixed up. You should note that map is a standalone function, not a member function of a list or any other type.

from __future__ import division
quickbrownfox1=['quick', 'brown', 'fox', 'jumps', 'lazy', 'dog']

def islistoflists(i):
    if isinstance(i, list):
        if len(i) > 0 and all(isinstance(t, list) for t in i):
            return True
    return False


def tf(tokens):

    print(islistoflists(tokens))

    abc = ([[x,tokens.count(x)] for x in set(tokens)])
    return list(map(lambda input: (input[0], input[1] / len(tokens)), abc))

print tf(quickbrownfox1)

To test if you have a list of lists, you can use isinstance to check the type of the parent object and if its a list and has at least one element in it, you can loop through them using isinstance to check if each child object is a list.

Note that I made your function return a list of tuples, implying that the items are read only, but you could make it return a list of lists by changing the line.

return list(map(lambda input: [input[0], input[1] / len(tokens)], abc))

If you look at it closely you'll see that a set of parenthesis have been substituted for square brackets, making each element a list.

If you have a older version of python 2 that does not support the from __future__ import division import you can uses the following workaround to force float division to occur.

return list(map(lambda input: (input[0], (input[1] * 1.0) / len(tokens)), abc))

Answer 2

Based on what I think you're asking you could do something like

token_size = len(tokens)
word_counter_list = {}
for word in tokens:
    if word in word_counter_list:
        word_counter_list[word] += 1
    else:
        word_counter_list[word] = 1

for word, amount in word_counter_list:
    print("The word " + word + " was used " + str(amount/token_size)

That being said the question isn't very clear since you're mentioning list type() but showing percentage of word frequency in a list

Answer 3

You should be able to do this fairly easily with a Counter :

$ python3
Python 3.4.2 (default, Oct  8 2014, 10:45:20) 
[GCC 4.9.1] on linux
Type "help", "copyright", "credits" or "license" for more information.
@>>> from collections import Counter
@>>> c = Counter(['quick', 'brown', 'fox', 'jumps', 'lazy', 'dog'])
@>>> total = sum(c.values())
@>>> result = dict()
@>>> for key, value in c.items():
@...   result[key] = value/total
@... 
@>>> result
{'dog': 0.16666666666666666, 'quick': 0.16666666666666666, 'fox': 0.16666666666666666, 'brown': 0.16666666666666666, 'jumps': 0.16666666666666666, 'lazy': 0.16666666666666666}

or, to make it super pythonic:

dict([ (key, value/total) for key,value in c.items() ])