How to add individual vlines to every subplot of seaborn FacetGrid

Question

I want to add a vertical line to every subplot to mark the individual launch date of each product. Every vertical line should display the date. But i am too beginner to figure this out. I tried .axvline as an example:

Here is the code:

g = sns.FacetGrid(df2, col='Product', hue='Vendor', col_wrap=4, height=3.5)
g = g.map(plt.plot, 'Date', 'Volumes')
g = g.map(plt.fill_between, 'Date', 'Volumes', alpha=0.2).set_titles("{col_name} Product")
g = g.set_titles("{col_name}")
g = g.set(xticks=[0, 12, 23])
g = g.set(xlabel='')

plt.axvline(x='Apr 19', color='r', linestyle=':')

I found the following apporaches, but i can't really make sense of it, or apply it to my own purposes:

Marking specific dates when visualizing a time series

Add vertical lines to Seaborn Facet Grid plots based on the occurrence of an event

I've created two lists with product names and corresponding launch dates:

product_names = ['Product A', 'Product B','Product C', 'Product D','Product E', 'Product F',
                 'Product G', 'Product H','Product I', 'Product J',]

launch_dates = ['2019-02-01', '2019-09-01', '2019-12-01', '2019-12-01',
                '2020-02-01', '2020-05-01', '2020-07-01', '2020-07-01',
                '2020-08-01', '2020-07-15']

launch_dates = [datetime.strptime(d, "%Y-%m-%d") for d in launch_dates]

So, how can I iterate through all facets to add the mentioned vertical line?

Sequence

Does this answer your question? How to draw vertical lines on a given plot – Tantalus

Answer 1

You could access the axes objects of the FacetGrid with g.axes.flat and add a line to each of them either at a given x-position or collected from a list for each individual facet:

import matplotlib.pyplot as plt
import seaborn as sns

tips = sns.load_dataset("tips")

g = sns.FacetGrid(tips, col="time", row="sex")
g.map_dataframe(sns.histplot, x="total_bill", binwidth=2)
g.set_axis_labels("Total bill", "Count")

line_position = [14, 23, 11, 39]

for ax, pos in zip(g.axes.flat, line_position):
    ax.axvline(x=pos, color='r', linestyle=':')

plt.tight_layout()
plt.show()

Sample output:

Spermatocyte

Now, how to add the vline to the legend? – Sisk

See, for instance, here – Spermatocyte

I’ll check that but I don’t think so. Apparently seaborn sets up the legend for a facet plot on ONE of the axes. So that would put it on the figure without the facet legend objects. – Sisk