pandas 统计数据频率函数value_counts

value_counts默认参数如下：

value_counts(values, sort=True, ascending=False, normalize=False, bins=None, dropna=True)

### Series类型
import pandas as pd
data=pd.Series(['python','java','python','php','php','java','python','java'])
print(data)
print('..........\n')
print(data.value_counts())
0    python
1      java
2    python
3       php
4       php
5      java
6    python
7      java
dtype: object
............

python    3
java      3
php       2

### DataFrame类型
import pandas as pd
data1={'key1':['python','java','python','php'],'key2':['php','java','python','SAS']}
b=pd.DataFrame(data1)
print(b)
print('............\n')
print(b.apply(pd.value_counts))
     key1    key2
0  python     php
1    java    java
2  python  python
3     php     SAS
............

        key1  key2
SAS      NaN     1
java     1.0     1
php      1.0     1
python   2.0     1