Matplotlib Formatting X-Axis Shows Jan-1-1970

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New to Matplotlib, trying to format dates on x axis. If I just use plt.xticks, the date is correct. But if I try to format the values using ax.xaxis.set_major_formatter, it changes my axis values to Jan-1-1970 based. I'm sure this is newbie stuff, thx for the bootstrap. (BTW, running in JupyterLabs notebook).

import pandas as pd
from datetime import date
import matplotlib.pyplot as plt
import matplotlib.dates as mdates
%matplotlib inline

# data to plot
#df_plot = df_dts[df_dts.dt>"8/17/2020"]
df_plot = pd.DataFrame({
    'dt': [date(2020,8,19), date(2020,8,20), date(2020,8,21), date(2020,8,22)],
    'open_cnt': [2,15,2,7],
    'close_cnt': [0,2,11,0]
})

# create plot
fig, ax = plt.subplots()
fig.set_size_inches(10, 5, forward=True)
index = np.arange(len(df_plot))
bar_width = 0.35
opacity = 0.8

rects1 = plt.bar(index, df_plot.open_cnt, bar_width, alpha=opacity, color='orange', label='Open')
rects2 = plt.bar(index + bar_width, df_plot.close_cnt, bar_width, alpha=opacity, color='g', label='Close')

plt.xlabel('Date')
plt.ylabel('Workitems')
plt.title('Open & Close Rates')
plt.xticks(index + bar_width/2, df_plot.dt)
ax.xaxis.set_major_formatter(mdates.DateFormatter('%b-%d-%y'))
plt.show()

enter image description here enter image description here

matplotlib python-3.x
2 Answers

Instead of messing up with formatter, set the index in your DataFrame to proper text representation of your dates and call plot.bar on this object:

fig, ax = plt.subplots(figsize=(10,5))
ax = df_plot.set_index(df_plot.dt.map(lambda s: s.strftime('%b-%d-%y')))\
    .plot.bar(ax=ax, legend=False, title='Open & Close Rates', rot=0,
    color=['orange', 'green'])
ax.set_xlabel('Date')
ax.set_ylabel('Workitems');

For your data I got the following picture:

enter image description here

As you can see, my code is more concise than yours.

user_73884770

If you don't want to change your original code much, you can simply do the transformation when you set the xticks.

df_plot['dt'] = pd.to_datetime(df_plot['dt'], format='%Y-%m-%d')
plt.xticks(index + bar_width/2, df_plot['dt'].dt.strftime('%b-%d-%y'))
user_103151630
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