How to Efficiently Annotate Pandas Bar Plots with Data Values?

Annotating Pandas Bar Plots with Data Values

When working with Pandas bar plots, it's often desirable to display the numerical values they represent. This article addresses the issue of annotating bars with rounded data values from the DataFrame.

Problem:

Consider the following DataFrame (df):

                 A         B
  value1  0.440922  0.911800
  value2  0.588242  0.797366

The goal is to annotate each bar with the corresponding rounded value, as illustrated in the image below:

[Image of a bar plot with annotated values]

Inefficient Approach:

One common approach to annotation is to use the annotate function. However, as the code sample below demonstrates, this approach positions annotations centered on the x-ticks:

ax = df.plot(kind='bar')
for idx, label in enumerate(list(df.index)):
    for acc in df.columns:
        value = np.round(df.ix[idx][acc], decimals=2)
        ax.annotate(value,
            (idx, value),
            xytext=(0, 15),
            textcoords='offset points')

Optimal Solution:

A more efficient solution is to obtain data from the axes' patches:

for p in ax.patches:
    ax.annotate(str(p.get_height()), (p.get_x() * 1.005, p.get_height() * 1.005))

This code extracts the bar height and positions the annotation slightly above the bar to center it.

Customization:

To customize the annotation, one can adjust the string formatting and offsets. For example:

for p in ax.patches:
    ax.annotate("{:.2f}".format(p.get_height()), (p.get_x() + p.get_width() / 2, p.get_height() * 1.005))

This centers the annotation over each bar and formats the height to two decimal places.

The above is the detailed content of How to Efficiently Annotate Pandas Bar Plots with Data Values?. For more information, please follow other related articles on the PHP Chinese website!