value_counts函数用于统计dataframe或series中不同数或字符串出现的次数
ascending=True时,按升序排列.
normalize=True时,可计算出不同字符出现的频率,画柱状图统计时可以用到.
df1= DataFrame( {"a":[3,4,5,6,2,3,4,4], "b":[2,4,5,6,5,4,3,4]} )
print(df1)
#dataframe要借助apply来应用value_counts()
print(df1.apply(pd.value_counts))
# map中括号内是series类型,key是a列的数,values是出现的次数
print(df1[‘a‘].map(df1[‘a‘].value_counts()))
a b 0 3 2 1 4 4 2 5 5 3 6 6 4 2 5 5 3 4 6 4 3 7 4 4 a b 2 1 1 3 2 1 4 3 3 5 1 2 6 1 1 0 2 1 3 2 1 3 1 4 1 5 2 6 3 7 3 Name: a, dtype: int64
https://blog.csdn.net/qq_20412595/article/details/79921849
https://blog.csdn.net/qq_42665335/article/details/81177699
原文：https://www.cnblogs.com/xxswkl/p/11022832.html
