如何在列表列表中查找项目的实例数

Question

I want part of a script I am writing to do something like this.

x=0
y=0
list=[["cat","dog","mouse",1],["cat","dog","mouse",2],["cat","dog","mouse",3]]

row=list[y]
item=row[x]
print list.count(item)

The problem is that this will print 0 because it isn't searching the individual lists.How can I make it return the total number of instances instead?

Answer 1

Search per sublist , adding up results per contained list with sum() :

sum(sub.count(item) for sub in lst)

Demo:

>>> lst = [["cat","dog","mouse",1],["cat","dog","mouse",2],["cat","dog","mouse",3]]
>>> item = 'cat'
>>> sum(sub.count(item) for sub in lst)
3

Answer 2

sum() is a builtin function for adding up its arguments.

The x.count(item) for x in list) is a "generator expression" (similar to a list comprehension) - a handy way to create and manage list objects in python.

item_count = sum(x.count(item) for x in list)

That should do it

Answer 3

Using collections.Counter and itertools.chain.from_iterable :

>>> from collections import Counter
>>> from itertools import chain
>>> lst = [["cat","dog","mouse",1],["cat","dog","mouse",2],["cat","dog","mouse",3]]
>>> count = Counter(item for item in chain.from_iterable(lst) if not isinstance(item, int))
>>> count
Counter({'mouse': 3, 'dog': 3, 'cat': 3})
>>> count['cat']
3

I filtered out the int s because I didn't see why you had them in the first place.