Date formatting with mdates in Matplotlib - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the date formatter from matplotlib.dates.

Matplotlib

from matplotlib.dates import [1]

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

ADateFormatter

Bdateparser

CDateLocator

Ddateformat

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'dateparser' which is not part of matplotlib.dates.

Confusing DateLocator with DateFormatter.

The DateFormatter class is used to format dates on matplotlib axes.

2fill in blank

medium

Complete the code to set the x-axis major formatter to display dates as 'Year-Month'.

Matplotlib

ax.xaxis.set_major_formatter([1]('%Y-%m'))

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

Amdates.DateFormatter

Bmdates.DateConverter

Cmdates.AutoDateFormatter

Dmdates.DateLocator

Attempts:

3 left

💡 Hint

Common Mistakes

Using DateLocator instead of DateFormatter.

Using AutoDateFormatter which auto-adjusts format but not with a fixed pattern.

DateFormatter formats dates according to the given string pattern.

3fill in blank

hard

Fix the error in the code to import matplotlib.dates as mdates.

Matplotlib

import matplotlib.[1] as mdates

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

Adatetime

Bdate

Cdates

Ddateutil

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'date' which is singular and incorrect.

Using unrelated modules like 'datetime' or 'dateutil'.

The correct submodule name is dates in matplotlib.

4fill in blank

hard

Fill both blanks to create a dictionary comprehension that maps dates to formatted strings using DateFormatter.

Matplotlib

formatted_dates = {date: [1]('%Y-%m-%d').format_data(date) for date in dates if date [2] datetime.date(2023, 1, 1)}

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

Amdates.DateFormatter

Bmdates.DateLocator

C>

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using DateLocator instead of DateFormatter for formatting.

Using '<' which filters dates before Jan 1, 2023.

Use DateFormatter to format dates and the '>' operator to filter dates after Jan 1, 2023.

5fill in blank

hard

Fill all three blanks to create a dictionary comprehension that maps date strings to datetime objects parsed with strptime.

Matplotlib

date_dict = [1]([2]: datetime.datetime.strptime([2], '%Y-%m-%d') for [2] in date_strings)

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

Adict

Bdate_str

Cdate_strings

Dlist

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'list' instead of 'dict' for the container.

Using 'date_strings' as the loop variable which is the list, not the item.

Use dict to create the dictionary, and date_str as the loop variable for date strings.

Practice

1. What is the main purpose of using mdates.DateFormatter in matplotlib?

easy

A. To customize how dates appear on the x-axis of a plot

B. To change the color of the plot lines

C. To add grid lines to the plot

D. To save the plot as an image file

Solution

1. Step 1: Understand the role of DateFormatter

   mdates.DateFormatter is used to format date labels on axes in matplotlib plots.

2. Step 2: Identify what DateFormatter customizes

   It changes how dates are shown, for example, showing only month and day or full date and time.

3. Final Answer:

   To customize how dates appear on the x-axis of a plot -> Option A

4. Quick Check:

   DateFormatter formats dates = A [OK]

Hint: DateFormatter changes date label style on axes [OK]

Common Mistakes:

• Confusing DateFormatter with plot styling functions
• Thinking it changes plot colors
• Assuming it saves files

2. Which of the following is the correct way to create a date formatter that shows dates as 'Year-Month-Day' using mdates.DateFormatter?

easy

A. mdates.DateFormatter('Y-m-d')

B. mdates.DateFormatter('%D-%M-%Y')

C. mdates.DateFormatter('%y/%M/%d')

D. mdates.DateFormatter('%Y-%m-%d')

Solution

1. Step 1: Recall strftime format codes

   Year is '%Y', month is '%m', day is '%d' in strftime formatting.

2. Step 2: Match correct format string

   mdates.DateFormatter('%Y-%m-%d') uses '%Y-%m-%d' which correctly formats as Year-Month-Day.

3. Final Answer:

   mdates.DateFormatter('%Y-%m-%d') -> Option D

4. Quick Check:

   Correct strftime codes = B [OK]

Hint: Use %Y, %m, %d for year, month, day in DateFormatter [OK]

Common Mistakes:

• Omitting % signs in format string
• Using uppercase M for minutes instead of month
• Mixing order of year, month, day

3. What will be the output on the x-axis labels if the following code is used?

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

dates = pd.date_range('2023-01-01', periods=3)
values = [10, 20, 15]

fig, ax = plt.subplots()
ax.plot(dates, values)
ax.xaxis.set_major_formatter(mdates.DateFormatter('%b %d'))
plt.show()

medium

A. Labels show dates as '01-01-2023', '01-02-2023', '01-03-2023'

B. Labels show dates as 'Jan 01', 'Jan 02', 'Jan 03'

C. Labels show dates as '2023-01-01', '2023-01-02', '2023-01-03'

D. Labels show dates as '01 Jan', '02 Jan', '03 Jan'

Solution

1. Step 1: Understand the format string '%b %d'

   '%b' is abbreviated month name (e.g., Jan), '%d' is day with leading zero.

2. Step 2: Apply format to dates

   Dates will appear as 'Jan 01', 'Jan 02', 'Jan 03' on x-axis labels.

3. Final Answer:

   Labels show dates as 'Jan 01', 'Jan 02', 'Jan 03' -> Option B

4. Quick Check:

   Format '%b %d' = 'Jan 01' style [OK]

Hint: Check strftime codes to predict label format [OK]

Common Mistakes:

• Confusing %b with %B (full month name)
• Expecting numeric month instead of abbreviated
• Ignoring leading zeros in day

4. Identify the error in this code snippet that tries to format dates on the x-axis:

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

dates = pd.date_range('2023-01-01', periods=3)
values = [5, 10, 15]

fig, ax = plt.subplots()
ax.plot(dates, values)
ax.xaxis.set_major_formatter(mdates.DateFormatter('%Y-%m-%d'))
ax.xaxis.set_major_locator(mdates.DayLocator())
plt.show()

medium

A. No error; code runs and formats dates correctly

B. Missing import for DayLocator

C. DateFormatter format string is invalid

D. Plot will fail because dates are not converted to numbers

Solution

1. Step 1: Check imports and usage

   All necessary imports are present, including mdates.DayLocator and DateFormatter.

2. Step 2: Verify date formatting and locator

   DateFormatter uses valid '%Y-%m-%d' format; DayLocator sets ticks daily. Dates are pandas datetime objects, which matplotlib handles.

3. Final Answer:

   No error; code runs and formats dates correctly -> Option A

4. Quick Check:

   Correct imports and usage = D [OK]

Hint: Check imports and valid format strings first [OK]

Common Mistakes:

• Assuming pandas dates need manual conversion
• Using wrong format codes in DateFormatter
• Forgetting to set locator for ticks

5. You want to plot daily sales data for a month and show x-axis labels only for Mondays in 'Month-Day' format (e.g., 'Jan-02'). Which combination of mdates functions should you use to achieve this?

hard

A. Use mdates.MonthLocator() and mdates.DateFormatter('%b')

B. Use mdates.DayLocator() and mdates.DateFormatter('%Y-%m-%d')

C. Use mdates.WeekdayLocator(byweekday=mdates.MO) and mdates.DateFormatter('%b-%d')

D. Use mdates.HourLocator() and mdates.DateFormatter('%H:%M')

Solution

1. Step 1: Choose locator for Mondays only

   mdates.WeekdayLocator(byweekday=mdates.MO) selects ticks only on Mondays.

2. Step 2: Format labels as 'Month-Day'

   mdates.DateFormatter('%b-%d') formats dates like 'Jan-02'.

3. Final Answer:

   Use mdates.WeekdayLocator(byweekday=mdates.MO) and mdates.DateFormatter('%b-%d') -> Option C

4. Quick Check:

   Monday ticks + 'Jan-02' format = C [OK]

Hint: Use WeekdayLocator with MO and DateFormatter '%b-%d' [OK]

Common Mistakes:

• Using DayLocator shows all days, not Mondays only
• MonthLocator shows monthly ticks, not weekly
• HourLocator is for time, not dates