矩阵数据结构如何获取各元素的数量

两个思路：

1. 在pandas里对dataframe进行统计

   >>> import pandas as pd
   >>> a=pd.DataFrame(data=[[1,2,3,4],[3,5,2,6],[6,2,8,4],[4,1,6,3]])
   >>> a
      0  1  2  3
   0  1  2  3  4
   1  3  5  2  6
   2  6  2  8  4
   3  4  1  6  3
   >>> a.stack().value_counts()
   6    3
   4    3
   3    3
   2    3
   1    2
   8    1
   5    1
   dtype: int64
   

2. 转换成list做统计

   >>> import collections
   >>> a = [1,1,1,1,2,2,2,2,3,3,4,5,5]
   >>> counter=collections.Counter(a)
   >>> print counter
   Counter({1: 4, 2: 4, 3: 2, 5: 2, 4: 1})