Draw a horizontal line line at specific position/annotate a Facetgrid in seaborn

问题

A have produced a boxplot with Facetgrid in seaborn the following way

# Import the dataset
tips = sns.load_dataset("tips")

# Plot using Facegrid, separated by smoke
plt.style.use('ggplot')
g = sns.FacetGrid(tips, col="smoker", size=5, aspect=1.5)
g.map(sns.boxplot, "sex", "total_bill", palette='viridis', order=['Male', 'Female'])
plt.show()

I now want to draw to distinct horizontal lines in each of the plot. For instance one horizontal line (with coordinated (0,10)) only in the left-hand side plot and another horizontal line (with coordinates (0,30)) only in the right-hand side plot.

How can I go about doing that?

回答1:

You can get a list of axes used in the FacetGrid using FacetGrid.axes which returns the axes used. You can then do all of the normal matplotlib operations using these axes, such as axhline for horizontal lines, or plt.text for putting text on the axes:

import seaborn as sns
import matplotlib.pyplot as plt
tips = sns.load_dataset("tips")

# Plot using Facegrid, separated by smoke
plt.style.use('ggplot')
g = sns.FacetGrid(tips, col="smoker", size=5, aspect=1.5)
g.map(sns.boxplot, "sex", "total_bill", palette='viridis', order=['Male', 'Female'])

ax1, ax2 = g.axes[0]

ax1.axhline(10, ls='--')
ax2.axhline(30, ls='--')

ax1.text(0.5,25, "Some text")
ax2.text(0.5,25, "Some text")

plt.show()

回答2:

Additionally, if you have a bunch of grids that you want to add one horizontal line (say at y=10) to all then you can just "map" the "plt.axhline" with your grid object:

import seaborn as sns
import matplotlib.pyplot as plt
tips = sns.load_dataset("tips")
# Plot using Facegrid, separated by smoke
plt.style.use('ggplot')
g = sns.FacetGrid(tips, col="smoker", size=5, aspect=1.5)
g.map(sns.boxplot, "sex", "total_bill", palette='viridis', order=['Male', 'Female'])

g.map(plt.axhline, y=10, ls='--', c='red')

回答3:

Just add to the top answer, if you want do the same thing with figures in cols.

g = sns.FacetGrid(df_long, col="variable", size=5, aspect=1.5,col_wrap=1,sharey=False)
# df_long is a long table with 3 variables
g.map(sns.boxplot, "label", "value", palette='Set2')
g.axes[0].axhline(1, ls='--',c='r')
g.axes[1].axhline(1, ls='--',c='r')
g.axes[2].axhline(0.5, ls='--',c='r')
g.map(plt.xticks, rotation=70) 
plt.show()

result

回答4:

There is axhline and hlines. Simple example:

chart = sns.relplot(x="x", y="y", kind="line", data=df)

chart.axes[0][0].axhline(y = 10, color='black', linewidth=2, alpha=.7)
chart.axes[0][0].hlines( y = 20, color='black', linewidth=2, alpha=.7, 
                         xmin = 30, xmax = 50)

Seems like hlines allows for min-max (documentation) but axhline doesn't.

来源：https://stackoverflow.com/questions/51891370/draw-a-horizontal-line-line-at-specific-position-annotate-a-facetgrid-in-seaborn

标签

python

seaborn

facet-grid