How to horizontally center a bar plot annotation?

问题

I am creating a bar chart like this:

gender = ['M', 'F']
numbers = [males,females]
bars = plt.bar(gender, numbers, width=0.1, bottom=None, align='center', data=None)
for i in range(len(numbers)):
    plt.annotate(str(numbers[i]), xy=(gender[i],numbers[i]))
plt.show()

I want to use plt.annotate to write the exact value on the top of the bar. However, the value is printed towards the right side. Is it possible to move it to the center?

回答1:

• In order to specify the horizontal alignment of the annotation, use the ha parameter
  • matplotlib: Text Properties & Layout
  • matplotlib: Annotations
  • matplotlib.pyplot.annotate
• As per the suggestion from JohanC
  • A trick is to use f'{value}\n' as a string and the unmodified value (or numbers) as y position, together with va='center'.
  • This also works with plt.text. Alternatively, plt.annotation accepts an offset in 'points' or in 'pixels'.

Option 1

• From lists of values & categories

import matplotlib.pyplot as plt

gender = ['M', 'F']
numbers = [1644, 1771]

plt.figure(figsize=(12, 6))
bars = plt.bar(gender, numbers, width=0.1, bottom=None, align='center', data=None)
for i in range(len(numbers)):
    plt.annotate(f'{numbers[i]}\n', xy=(gender[i], numbers[i]), ha='center', va='center')

Option 2

• From a pandas.DataFrame
• Use pandas.DataFrame.iterrows to extract the x and y location needed for the annotations.
  • x being the categorical 'gender' value
  • y being the numeric 'value'

import pandas as pd
import matplotlib.pyplot as plt

df = pd.DataFrame({'value': [1771, 1644], 'gender': ['F', 'M']})

plt.figure(figsize=(12, 6))
bars = plt.bar(df.gender, df.value, width=0.1, bottom=None, align='center', data=None)
for idx, (value, gender) in df.iterrows():
    plt.annotate(f'{value}\n', xy=(gender, value), ha='center', va='center')

Plot Output

来源：https://stackoverflow.com/questions/63209883/how-to-horizontally-center-a-bar-plot-annotation