datetime x-axis matplotlib labels causing uncontrolled overlap

Question

I\'m trying to plot a pandas series with a \'pandas.tseries.index.DatetimeIndex\'. The x-axis label stubbornly overlap, and I cannot make them p

Answer 1

In your situation, the easiest would be to manually create labels and spacing, and apply that using ax.xaxis.set_major_formatter.

Here's a possible solution:

Since no sample data was provided, I tried to mimic the structure of your dataset in a dataframe with some random numbers.

The setup:

# imports
import pandas as pd
import numpy as np
import matplotlib.pyplot as plt
import matplotlib.dates as mdates
import matplotlib.ticker as ticker

# A dataframe with random numbers ro run tests on
np.random.seed(123456)
rows = 100
df = pd.DataFrame(np.random.randint(-10,10,size=(rows, 1)), columns=['error'])
datelist = pd.date_range(pd.datetime(2017, 1, 1).strftime('%Y-%m-%d'), periods=rows).tolist()
df['dates'] = datelist 
df = df.set_index(['dates'])
df.index = pd.to_datetime(df.index)

test_df = df.copy(deep = True)

# Plot of data that mimics the structure of your dataset
ax = test_df[(test_df.index.year ==2017) ]['error'].plot(kind="bar")
ax.figure.autofmt_xdate()
plt.figure(figsize=(15,8))

A possible solution:

test_df = df.copy(deep = True)
ax = test_df[(test_df.index.year ==2017) ]['error'].plot(kind="bar")
plt.figure(figsize=(15,8))

# Make a list of empty myLabels
myLabels = ['']*len(test_df.index)

# Set labels on every 20th element in myLabels
myLabels[::20] = [item.strftime('%Y - %m') for item in test_df.index[::20]]
ax.xaxis.set_major_formatter(ticker.FixedFormatter(myLabels))
plt.gcf().autofmt_xdate()

# Tilt the labels
plt.setp(ax.get_xticklabels(), rotation=30, fontsize=10)
plt.show()

You can easily change the formatting of labels by checking strftime.org

Answer 2

A pandas bar plot is a categorical plot. It shows one bar for each index at integer positions on the scale. Hence the first bar is at position 0, the next at 1 etc. The labels correspond to the dataframes' index. If you have 100 bars, you'll end up with 100 labels. This makes sense because pandas cannot know if those should be treated as categories or ordinal/numeric data.

If instead you use a normal matplotlib bar plot, it will treat the dataframe index numerically. This means the bars have their position according to the actual dates and labels are placed according to the automatic ticker.

import pandas as pd
import numpy as np; np.random.seed(42)
import matplotlib.pyplot as plt

datelist = pd.date_range(pd.datetime(2017, 1, 1).strftime('%Y-%m-%d'), periods=42).tolist()
df = pd.DataFrame(np.cumsum(np.random.randn(42)), 
                  columns=['error'], index=pd.to_datetime(datelist))

plt.bar(df.index, df["error"].values)
plt.gcf().autofmt_xdate()
plt.show()

The advantage is then in addition that matplotlib.dates locators and formatters can be used. E.g. to label each first and fifteenth of a month with a custom format,

import pandas as pd
import numpy as np; np.random.seed(42)
import matplotlib.pyplot as plt
import matplotlib.dates as mdates

datelist = pd.date_range(pd.datetime(2017, 1, 1).strftime('%Y-%m-%d'), periods=93).tolist()
df = pd.DataFrame(np.cumsum(np.random.randn(93)), 
                  columns=['error'], index=pd.to_datetime(datelist))

plt.bar(df.index, df["error"].values)
plt.gca().xaxis.set_major_locator(mdates.DayLocator((1,15)))
plt.gca().xaxis.set_major_formatter(mdates.DateFormatter("%d %b %Y"))
plt.gcf().autofmt_xdate()
plt.show()