[Matplotlib-users] bar plot with datetime x axis

[Steve Aplin]

Hello everyone,

Having a bit of an adventure controlling the display of the x axis when
plotting a pandas dataframe or series using pandas plot(), as in
df.plot(kind='bar') or s.plot(kind='bar').

Here's the head of one column:

1996-01-01    180.0
1997-01-01    159.0
1998-01-01    159.0
1999-01-01    152.0
2000-01-01    121.0
Name: column A, dtype: float64


... and here's its index:

DatetimeIndex(['1996-01-01', '1997-01-01', '1998-01-01', '1999-01-01',
               '2000-01-01', ... ],
              dtype='datetime64[ns]', freq=None)

I want to show a bunch of subplots, so my code looks like this:

> from datetime import datetime
> import matplotlib.pyplot as plt
> import pandas as pd
> import numpy as np
> import matplotlib.dates as mdates
> %matplotlib inline
>
> fig, axs = plt.subplots(9,2,figsize=(20,20),sharex=True)
> for i,col in enumerate(df):
>     ax = df[col].plot(kind='bar',ax=axs[i,0])
>
   etc.


... which gives an x tick value for each index item (i.e. each bar), in
full datetime format (YYYY-MM-DD 00:00:00), rotated 90 degrees.

I don't want full datetime format, I just want the year portion. Googling
the issue led me to trying this:

fig.autofmt_xdate()
>

... which rotates the labels, but still in full datetime format.

So I tried adding

> formatter = mdates.DateFormatter('%Y')
> ax.xaxis.set_major_formatter(formatter)
>

which throws this error:

ValueError: DateFormatter found a value of x=0, which is an illegal
date.  This usually occurs because you have not informed the axis that
it is plotting dates, e.g., with ax.xaxis_date()

... which is a bit confusing, since the index is a pandas datetimeindex.

Any ideas about how I could get my xaxis to not show just the year portion?

Thanks in advance!

Stephen E. Aplin
Ottawa Canada
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