如何在Python中生成多个模式？

Question

基本上，我就是想知道怎么在Python中从一个列表里找出出现次数最多的数字，也就是众数。不管这个列表有没有多个众数都没关系。

像这样：

def print_mode (thelist):
  counts = {}
  for item in thelist:
    counts [item] = counts.get (item, 0) + 1
  maxcount = 0
  maxitem = None
  for k, v in counts.items ():
    if v > maxcount:
      maxitem = k
      maxcount = v
  if maxcount == 1:
    print "All values only appear once"
  if counts.values().count (maxcount) > 1:
    print "List has multiple modes"
  else:
    print "Mode of list:", maxitem

不过，我希望它返回的不是“所有值只出现一次”或者“列表有多个众数”这样的字符串，而是我想要的那些实际的整数。

Answer 1

在Python 3.8的新统计模块里，有一个专门用来处理这个的函数：

import statistics as s
print("mode(s): ",s.multimode([1,1,2,2]))

输出结果：众数是：[1, 2]

Answer 2

def mode(arr):

if len(arr) == 0:
    return []

frequencies = {}

for num in arr:
    frequencies[num] = frequencies.get(num,0) + 1

mode = max([value for value in frequencies.values()])

modes = []

for key in frequencies.keys():
    if frequencies[key] == mode:
        modes.append(key)

return modes

这段代码可以处理任何列表。确保列表里的元素都是数字。

Answer 3

先创建一个 Counter，然后找出出现频率最高的元素：

from collections import Counter
from itertools import groupby

l = [1,2,3,3,3,4,4,4,5,5,6,6,6]

# group most_common output by frequency
freqs = groupby(Counter(l).most_common(), lambda x:x[1])
# pick off the first group (highest frequency)
print([val for val,count in next(freqs)[1]])
# prints [3, 4, 6]