Labeling boxplot in seaborn with median value

Question

How can I label each boxplot in a seaborn plot with the median value?

E.g.

import seaborn as sns
sns.set_style(\"whitegrid\")
tips = sns.load_dataset         


        

Answer 1

This can also be achieved by deriving median from the plot itself without exclusively computing median from data

box_plot = sns.boxplot(x="day", y="total_bill", data=tips)

ax = box_plot.axes
lines = ax.get_lines()
categories = ax.get_xticks()

for cat in categories:
    # every 4th line at the interval of 6 is median line
    # 0 -> p25 1 -> p75 2 -> lower whisker 3 -> upper whisker 4 -> p50 5 -> upper extreme value
    y = round(lines[4+cat*6].get_ydata()[0],1) 

    ax.text(
        cat, 
        y, 
        f'{y}', 
        ha='center', 
        va='center', 
        fontweight='bold', 
        size=10,
        color='white',
        bbox=dict(facecolor='#445A64'))

box_plot.figure.tight_layout()

Answer 2

I love when people include sample datasets!

import seaborn as sns

sns.set_style("whitegrid")
tips = sns.load_dataset("tips")
box_plot = sns.boxplot(x="day",y="total_bill",data=tips)

medians = tips.groupby(['day'])['total_bill'].median()
vertical_offset = tips['total_bill'].median() * 0.05 # offset from median for display

for xtick in box_plot.get_xticks():
    box_plot.text(xtick,medians[xtick] + vertical_offset,medians[xtick], 
            horizontalalignment='center',size='x-small',color='w',weight='semibold')

Answer 3

Based on ShikjarDua's excellent approach, I created a version which works independent of tick positions. This comes in handy when dealing with grouped data in seaborn (i.e. hue=parameter). Additionally, I added an explicit switch for fliers, which changes the lines per drawn box.

import seaborn as sns
import matplotlib.pyplot as plt
import matplotlib.patheffects as path_effects


def main():
    sns.set_style("whitegrid")
    tips = sns.load_dataset("tips")
    # optionally disable fliers
    showfliers = False
    # plot data and create median labels
    box_plot = sns.boxplot(x="day", y="total_bill", data=tips,
                           showfliers=showfliers, hue="sex")
    create_median_labels(box_plot.axes, showfliers)
    plt.show()


def create_median_labels(ax, has_fliers):
    lines = ax.get_lines()
    # depending on fliers, toggle between 5 and 6 lines per box
    lines_per_box = 5 + int(has_fliers)
    # iterate directly over all median lines, with an interval of lines_per_box
    # this enables labeling of grouped data without relying on tick positions
    for median_line in lines[4:len(lines):lines_per_box]:
        # get center of median line
        mean_x = sum(median_line._x) / len(median_line._x)
        mean_y = sum(median_line._y) / len(median_line._y)
        # print text to center coordinates
        text = ax.text(mean_x, mean_y, f'{mean_y:.1f}',
                       ha='center', va='center',
                       fontweight='bold', size=10, color='white')
        # create small black border around white text
        # for better readability on multi-colored boxes
        text.set_path_effects([
            path_effects.Stroke(linewidth=3, foreground='black'),
            path_effects.Normal(),
        ])


if __name__ == '__main__':
    main()