来自四个Pandas系列的多个箱线图抛出值错误

Question

当使用plt.boxplot()从熊猫四个独立的熊猫系列中绘制四个箱线图时，我得到以下ValueError：

`ValueError`: The truth value of a DataFrame is ambiguous. Use `a.empty`, `a.bool()`, `a.item()`, `a.any()` or `a.all()`.

如果您对这里发生的事情有任何想法，我们将不胜感激

import matplotlib.pyplot as plt
import numpy as np
import pandas as pd

ped_df = pd.read_csv("C:/NewMapsPlus/Map674/map674-module-04-zac-stanley/notebooks/data/AvgHourlyUserAllTypes.csv")

btel = ped_df[['BTEL_Pedestrians']]
cf = ped_df[['CF1_Pedestrians']]
dr = ped_df[['DR1_Pedestrians']]
hh = ped_df[['HawkHill_Pedestrians']]

plt.figure(figsize=(15,6))
plt.boxplot(btel, cf, dr, hh)