无法将第二个绘图添加到日志转换图

根据下面的代码,绘制历史价格数据的对数转换工作正常,但是当任何第二个图(例如收盘价)添加到图中时,对数转换被绘制为ts=0?!

代码:

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

df = pd.read_csv('historical_price_data.csv')
df = df[::-1]
df['Date'] = pd.to_datetime(df.Date, infer_datetime_format=True) 

# Set index to Date returns KeyError: "['Date'] not in index"
# df.set_index('Date', inplace=True)
df.sort_index(inplace=True)

# Log Transform 
log_transform = df['Close']
df['log'] = np.log(log_transform)

# Log transform plots fine by itself
ax = df[['Date', 'log']].plot(figsize=(14, 7), x='Date')

# Adding another plot to the figure results in log_transform being set to 0 !
ax = df[['Date', 'Close']].plot(figsize=(14, 7), x='Date', ax=ax)

plot.show()

只需注意,用一个loc而不是2来绘制它们会导致日志转换行被压缩为0时出现相同的问题:

ax = df[['Date', 'log', 'Close']].plot(x='Date')