Highlighting date ranges in Matplotlib - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of date range highlighting with matplotlib

What will be the output of this code snippet that highlights a date range on a line plot?

Matplotlib

import matplotlib.pyplot as plt
import pandas as pd
import numpy as np

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

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

A A line plot with a yellow transparent vertical band from Jan 3 to Jan 6

B A line plot with a red transparent vertical band from Jan 1 to Jan 10

C A line plot with no highlighted area

D A line plot with a yellow transparent horizontal band from 3 to 6

💡 Hint

Look at the function plt.axvspan and the dates it uses.

The plt.axvspan function highlights a vertical span between two x-axis values. Here, it highlights from 2024-01-03 to 2024-01-06 with a yellow transparent color.

❓ data_output

intermediate

Number of points inside highlighted date range

Given the following data and highlighted date range, how many data points fall inside the highlighted range?

Matplotlib

import pandas as pd
import numpy as np

dates = pd.date_range('2024-01-01', periods=15)
values = np.random.rand(15)
data = pd.DataFrame({'date': dates, 'value': values})
highlight_start = pd.Timestamp('2024-01-05')
highlight_end = pd.Timestamp('2024-01-10')

inside_points = data[(data['date'] >= highlight_start) & (data['date'] <= highlight_end)]
print(len(inside_points))

A 6

B 5

C 7

D 10

💡 Hint

Count dates from Jan 5 to Jan 10 inclusive.

Dates from 2024-01-05 to 2024-01-10 inclusive are 6 days, so 6 points fall inside the range.

❓ visualization

advanced

Identify the correct highlighted date range in plot

Which option shows the correct code to highlight the date range from 2024-02-10 to 2024-02-15 on a time series plot?

Matplotlib

import matplotlib.pyplot as plt
import pandas as pd
import numpy as np

dates = pd.date_range('2024-02-01', periods=20)
values = np.random.randn(20).cumsum()
plt.plot(dates, values)
# Highlight code here
plt.show()

A

plt.axvline(pd.Timestamp('2024-02-10'), color='green')
plt.axvline(pd.Timestamp('2024-02-15'), color='green')

B plt.axhspan(pd.Timestamp('2024-02-10'), pd.Timestamp('2024-02-15'), color='green', alpha=0.2)

C plt.axvspan(pd.Timestamp('2024-02-10'), pd.Timestamp('2024-02-15'), color='green', alpha=0.2)

D plt.fill_between(dates, values, where=(dates >= '2024-02-10') & (dates <= '2024-02-15'), color='green', alpha=0.2)

💡 Hint

Use vertical span to highlight date ranges on x-axis.

plt.axvspan highlights a vertical band between two x-axis dates. axhspan highlights horizontal bands (y-axis).

🔧 Debug

advanced

Identify the error in date range highlighting code

What error will this code produce when trying to highlight a date range?

Matplotlib

import matplotlib.pyplot as plt
import pandas as pd
import numpy as np

dates = pd.date_range('2024-03-01', periods=10)
values = np.arange(10)
plt.plot(dates, values)
plt.axvspan('2024-03-03', '2024-03-06', color='blue', alpha=0.3)
plt.show()

A TypeError: unsupported operand type(s) for -: 'str' and 'str'

B No error, plot shows highlighted range correctly

C NameError: name 'pd' is not defined

D ValueError: could not convert string to float: '2024-03-03'

💡 Hint

Check the types passed to plt.axvspan for date values.

plt.axvspan expects numeric or datetime objects for x-axis limits. Passing strings causes a ValueError during internal conversion to float.

🚀 Application

expert

Calculate total duration of multiple highlighted date ranges

Given multiple highlighted date ranges, what is the total number of days covered without counting overlaps twice?

Matplotlib

import pandas as pd

ranges = [
    (pd.Timestamp('2024-04-01'), pd.Timestamp('2024-04-05')),
    (pd.Timestamp('2024-04-04'), pd.Timestamp('2024-04-10')),
    (pd.Timestamp('2024-04-12'), pd.Timestamp('2024-04-15'))
]

# Calculate total days covered by these ranges without double counting overlaps

A 15

B 14

C 12

D 13

💡 Hint

Merge overlapping intervals before summing durations.

The first two ranges overlap from Apr 4 to Apr 5. Merging them gives Apr 1 to Apr 10 (10 days). The third range is Apr 12 to Apr 15 (4 days). Total is 10 + 4 = 14 days, but since end dates are inclusive, days count is (10 - 1 + 1) + (15 - 12 + 1) = 10 + 4 = 14 days. However, careful calculation shows Apr 1 to Apr 10 is 10 days, Apr 12 to Apr 15 is 4 days, total 14 days. So correct answer is 14.