Date locators for tick spacing in Matplotlib - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the correct date locator for setting tick spacing by days.

Matplotlib

from matplotlib.dates import [1]

Drag options to blanks, or click blank then click option'

AMinuteLocator

BHourLocator

CSecondLocator

DDayLocator

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing HourLocator or MinuteLocator which set ticks by smaller time units.

Using SecondLocator which is for seconds, not days.

The DayLocator is used to set tick marks spaced by days on a date axis.

2fill in blank

medium

Complete the code to create a date locator that places ticks every 3 days.

Matplotlib

locator = [1](interval=3)

Drag options to blanks, or click blank then click option'

ADayLocator

BMonthLocator

CWeekdayLocator

DHourLocator

Attempts:

3 left

💡 Hint

Common Mistakes

Using MonthLocator which controls ticks by months.

Using WeekdayLocator which is for specific weekdays.

DayLocator with interval=3 places ticks every 3 days.

3fill in blank

hard

Fix the error in the code to set major ticks every Monday using the correct weekday locator.

Matplotlib

from matplotlib.dates import WeekdayLocator, MO
locator = WeekdayLocator(byweekday=[1])

Drag options to blanks, or click blank then click option'

AMO

BSU

C0

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Using numbers like 0 or 1 instead of the constant MO.

Using SU which is the wrong day.

The WeekdayLocator uses constants like MO to specify weekdays.

4fill in blank

hard

Fill both blanks to create a locator that sets ticks every 2 weeks on Wednesday.

Matplotlib

from matplotlib.dates import WeekdayLocator, [1]
locator = WeekdayLocator(byweekday=[2], interval=2)

Drag options to blanks, or click blank then click option'

AWE

BTH

DFR

Attempts:

3 left

💡 Hint

Common Mistakes

Using different weekdays for import and argument.

Using weekdays other than Wednesday.

Import WE and use it as the byweekday argument to set ticks every 2 weeks on Wednesday.

5fill in blank

hard

Fill all three blanks to create a dictionary comprehension that maps dates to values only for dates after January 1, 2020.

Matplotlib

filtered_data = {date: value for date, value in data.items() if date [1] datetime(2020, 1, 1) and value [2] 0 and isinstance(value, [3])}

Drag options to blanks, or click blank then click option'

A>

B>=

Cint

Dfloat

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' or '<=' which would select wrong dates.

Using wrong type like float instead of int.

The comprehension filters dates greater than January 1, 2020, values greater or equal to 0, and values that are integers.

Practice

1. What is the main purpose of using DateLocator classes in matplotlib when plotting dates?

easy

A. To add grid lines to the plot

B. To change the color of the plot lines

C. To set the plot title automatically

D. To control where date ticks appear on the axis

Solution

1. Step 1: Understand the role of DateLocator

   DateLocator classes in matplotlib are designed to specify the positions of ticks on date axes.

2. Step 2: Identify the correct purpose

   They do not affect colors, grid lines, or titles but control tick placement for dates.

3. Final Answer:

   To control where date ticks appear on the axis -> Option D

4. Quick Check:

   DateLocator controls tick positions = C [OK]

Hint: DateLocator sets tick positions on date axes [OK]

Common Mistakes:

• Confusing tick placement with plot styling
• Thinking DateLocator changes colors or titles
• Assuming DateLocator adds grid lines

2. Which of the following is the correct way to import the MonthLocator from matplotlib's dates module?

easy

A. import matplotlib.MonthLocator

B. from matplotlib.dates import MonthLocator

C. from matplotlib import MonthLocator

D. import MonthLocator from matplotlib.dates

Solution

1. Step 1: Recall correct import syntax for specific classes

   In Python, to import a class from a submodule, use 'from module import ClassName'.

2. Step 2: Match with matplotlib.dates module

   MonthLocator is in matplotlib.dates, so the correct import is 'from matplotlib.dates import MonthLocator'.

3. Final Answer:

   from matplotlib.dates import MonthLocator -> Option B

4. Quick Check:

   Correct import syntax = A [OK]

Hint: Use 'from module import Class' for specific imports [OK]

Common Mistakes:

• Using 'import' without 'from' for submodules
• Incorrect module path or syntax
• Confusing import order or keywords

3. What will be the effect of this code snippet on the x-axis ticks?

import matplotlib.pyplot as plt
import matplotlib.dates as mdates
import pandas as pd

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

fig, ax = plt.subplots()
ax.plot(dates, values)
ax.xaxis.set_major_locator(mdates.DayLocator(interval=3))
plt.show()

medium

A. Ticks will appear every 3 days on the x-axis

B. Ticks will appear every day on the x-axis

C. Ticks will appear every 3 months on the x-axis

D. Ticks will not appear on the x-axis

Solution

1. Step 1: Understand DayLocator with interval=3

   DayLocator places ticks on days. Setting interval=3 means ticks every 3 days.

2. Step 2: Apply to the plot

   The x-axis will show ticks spaced by 3 days along the date range.

3. Final Answer:

   Ticks will appear every 3 days on the x-axis -> Option A

4. Quick Check:

   DayLocator(interval=3) = ticks every 3 days [OK]

Hint: DayLocator(interval=3) means ticks every 3 days [OK]

Common Mistakes:

• Confusing days with months or weeks
• Ignoring the interval parameter
• Expecting no ticks due to interval

4. Identify the error in this code that tries to set weekly ticks on Mondays:

import matplotlib.pyplot as plt
import matplotlib.dates as mdates
import pandas as pd

dates = pd.date_range('2024-01-01', periods=14)
values = range(14)

fig, ax = plt.subplots()
ax.plot(dates, values)
ax.xaxis.set_major_locator(mdates.WeekdayLocator(byweekday=mdates.MONDAY, interval=1))
plt.show()

medium

A. Dates must be strings, not pandas Timestamps

B. WeekdayLocator does not accept byweekday argument

C. mdates.MONDAY does not exist; use mdates.MO instead

D. interval cannot be set to 1

Solution

1. Step 1: Check WeekdayLocator constants

   matplotlib.dates does not define MONDAY; the constant for Monday is MO (which is 0).

2. Step 2: Identify correct usage

   Replace mdates.MONDAY with mdates.MO. A single weekday constant does not need a list or tuple.

3. Final Answer:

   mdates.MONDAY does not exist; use mdates.MO instead -> Option C

4. Quick Check:

   mdates.MO for Monday (not MONDAY) = D [OK]

Hint: mdates.MO for Monday, not MONDAY [OK]

Common Mistakes:

• Using MONDAY instead of MO
• Misunderstanding weekday constant names (MO, TU, etc.)
• Confusing with full day names like dateutil

5. You want to plot daily data for 6 months but only show ticks on the first day of each month. Which locator and interval setting achieves this best?

hard

A. Use MonthLocator(bymonthday=1, interval=1)

B. Use DayLocator(interval=30)

C. Use WeekdayLocator(byweekday=mdates.MONDAY, interval=4)

D. Use MonthLocator(bymonthday=15, interval=1)

Solution

1. Step 1: Understand requirement for ticks on first day of each month

   MonthLocator with bymonthday=1 places ticks on the first day of each month.

2. Step 2: Check interval for monthly spacing

   Setting interval=1 ensures ticks appear every month, exactly on day 1.

3. Final Answer:

   Use MonthLocator(bymonthday=1, interval=1) -> Option A

4. Quick Check:

   MonthLocator with bymonthday=1 = ticks on first day monthly [OK]

Hint: MonthLocator with bymonthday=1 shows first day ticks [OK]

Common Mistakes:

• Using DayLocator with fixed interval ignores month boundaries
• Choosing wrong day like 15 instead of 1
• Using WeekdayLocator which targets weekdays, not month start