Apr 8, 2010 · from collections import Counter from collections import defaultdict import numpy import operator import pandas import perfplot def counter(a): return Counter(a) def count(a): return dict((i, a.count(i)) for i in set(a)) def bincount(a): return numpy.bincount(a) def pandas_value_counts(a): return pandas.Series(a).value_counts() def occur_dict(a ...

Nov 11, 2009 · item_count = 0 for item in list: item_count += 1 return item_count count([1,2,3,4,5]) (The list object must be iterable, implied by the for..in stanza.) The lesson here for new programmers is: You can’t get the number of items in a list without counting them at some point.

Apr 23, 2014 · Python: count repeated elements in the list [duplicate] ... if you use a 'set' for get unique values in ...

Sep 12, 2019 · std::multiset allows storing multiple distinct but comparatively equal values, which is what makes it so useful. (For example, you can compare a list of locations by their temperature, and use a multiset to look up all locations at a specific temperature or temperature range, while getting the fast insertions of a set.)

Oct 7, 2012 · I have a list of Booleans: [True, True, False, False, False, True] and I am looking for a way to count the number of True in the list (so in the example above, I want the return to be 3.) I have ...

@KritikaRajain For each unique element in the list you iterate over the whole list to generate a count (quadratic in the number of unique elements in the list). Instead, you can iterate over the list once and count up the number of each unique element (linear in the size of the list).

May 10, 2012 · If you are using NumPy (as in ludaavic's answer), for large arrays you'll probably want to use NumPy's sum function rather than Python's builtin sum for a significant speedup -- e.g., a >1000x speedup for 10 million element arrays on my laptop:

May 31, 2010 · Is there any efficient way in python to count the times an array of numbers is between certain intervals? the number of intervals i will be using may get quite large like: mylist = [4,4,1,18,2,15...

Nov 9, 2010 · Unfortunately, it seems this is the first google result for python list check number of elements, instead of the linked question that this duplicates. – Drise Commented Dec 14, 2017 at 17:03

The main difference between groupby.count and groupby.size is that count counts only non-NaN values while size returns the length (which includes NaN), if the column has NaN values. value_counts() is equivalent to groupby.count by default but can become equivalent to groupby.size if dropna=False, i.e. df['col'].value_counts(dropna=False).