运算 - 选择后.mean() - 平均值

import numpy as np
import pandas as pd
df = pd.DataFrame(data=[{"A":"1", "B":"3"}, {"A":"3", "B":"2"}, {"A":"2", "B":"1"}])
df = pd.DataFrame(data=[{"A":1, "B":3}, {"A":3, "B":2}, {"A":2, "B":1}])

df['A'] = df['A'].astype("float")
df['B'] = df['B'].astype("float")
都要转成float
# mean()平均值  median()中位数  max()最大值  min()最小值  sum()求和  std()标准差
print(df.mean())  # 每一列平均值 (Series类型)

A    2.0
B    2.0
dtype: float64