Highlighting date ranges in Matplotlib - Step-by-Step Execution

Concept Flow - Highlighting date ranges

Prepare date data

↓

Plot time series

↓

Define date range to highlight

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Use ax.axvspan() to add highlight

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Show plot with highlighted range

This flow shows how to plot dates and highlight a specific date range on the plot using matplotlib.

Execution Sample

Matplotlib

import matplotlib.pyplot as plt
import pandas as pd

dates = pd.date_range('2024-01-01', periods=10)
values = range(10)

plt.plot(dates, values)
plt.axvspan(pd.Timestamp('2024-01-03'), pd.Timestamp('2024-01-06'), color='yellow', alpha=0.3)
plt.show()

Plot a simple time series and highlight the date range from 2024-01-03 to 2024-01-06 with a yellow transparent box.

Execution Table

Step	Action	Input/Parameters	Result/Output
1	Create date range	'2024-01-01' to 10 days	dates = 2024-01-01 to 2024-01-10
2	Create values	range(10)	values = [0,1,2,3,4,5,6,7,8,9]
3	Plot dates vs values	dates, values	Line plot with 10 points
4	Highlight date range	start=2024-01-03, end=2024-01-06, color=yellow, alpha=0.3	Yellow transparent box from 2024-01-03 to 2024-01-06 on plot
5	Show plot	None	Plot window opens with line and highlighted range

💡 Plot displayed with highlighted date range; execution ends.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4	Final
dates	None	DatetimeIndex from 2024-01-01 to 2024-01-10	Same	Same	Same	Same
values	None	None	[0,1,2,3,4,5,6,7,8,9]	Same	Same	Same

Key Moments - 3 Insights

Why do we use pd.Timestamp for the start and end dates in axvspan?

Matplotlib needs dates in a datetime format it understands. pd.Timestamp converts strings to datetime objects compatible with the plot's x-axis. See execution_table step 4.

What does the alpha parameter do in axvspan?

Alpha controls transparency of the highlight color. Lower alpha means more transparent. This lets us see the plot lines under the highlight. See execution_table step 4.

Can we highlight multiple date ranges on the same plot?

Yes, by calling axvspan multiple times with different start and end dates before plt.show(). Each call adds another highlighted area.

Visual Quiz - 3 Questions

Look at the execution_table at step 4, what color is used to highlight the date range?

A Blue

B Red

C Yellow

D Green

💡 Hint

Check the 'Input/Parameters' column in step 4 of execution_table.

According to variable_tracker, what is the value of 'values' after step 2?

A [0,1,2,3,4,5,6,7,8,9]

B [1,2,3,4,5,6,7,8,9,10]

C None

D Range object

💡 Hint

Look at the 'values' row under 'After Step 2' in variable_tracker.

At which step does the plot window open showing the highlighted date range?

A Step 3

B Step 5

C Step 4

D After all steps

💡 Hint

Refer to the 'Result/Output' column in execution_table step 5.

Concept Snapshot

Highlighting date ranges in matplotlib:
- Use plt.plot() to plot dates vs values.
- Use plt.axvspan(start_date, end_date, color, alpha) to highlight range.
- Dates must be datetime objects (e.g., pd.Timestamp).
- Alpha controls transparency of highlight.
- Call plt.show() to display the plot.

Full Transcript

This lesson shows how to highlight date ranges on a matplotlib plot. First, we create a date range and some values. Then we plot these dates against values as a line. Next, we define a start and end date for the highlight and use axvspan with color and transparency to add a colored box behind the line plot. Finally, we show the plot window with the highlighted date range visible. Key points include converting date strings to datetime objects and adjusting transparency with alpha. Multiple highlights can be added by calling axvspan multiple times before showing the plot.