Bar width and positioning in Matplotlib - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to set the width of the bars to 0.5.

Matplotlib

import matplotlib.pyplot as plt

x = [1, 2, 3]
heights = [4, 5, 6]
plt.bar(x, heights, width=[1])
plt.show()

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

A0

B1.5

C2

D0.5

Attempts:

3 left

💡 Hint

Common Mistakes

Using width greater than 1 makes bars overlap.

Setting width to 0 makes bars invisible.

The width parameter controls the thickness of the bars. Setting it to 0.5 makes the bars half as wide as the default.

2fill in blank

medium

Complete the code to position bars at x-coordinates shifted by 0.3 to the right.

Matplotlib

import matplotlib.pyplot as plt

x = [1, 2, 3]
heights = [4, 5, 6]
plt.bar([i + [1] for i in x], heights, width=0.5)
plt.show()

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

A0.3

B0.1

C-0.3

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Using negative values shifts bars left instead of right.

Using 1 shifts bars too far.

Adding 0.3 shifts the bars to the right by 0.3 units on the x-axis.

3fill in blank

hard

Fix the error in the code to correctly position two sets of bars side by side.

Matplotlib

import matplotlib.pyplot as plt

x = [1, 2, 3]
heights1 = [4, 5, 6]
heights2 = [3, 4, 5]
width = 0.4
plt.bar(x, heights1, width=width, label='A')
plt.bar([i [1] width for i in x], heights2, width=width, label='B')
plt.legend()
plt.show()

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

A*

B-

C+

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Using subtraction shifts bars left, overlapping the first set.

Using multiplication or division causes errors or wrong positions.

Adding width shifts the second set of bars to the right, placing them side by side.

4fill in blank

hard

Fill both blanks to create a dictionary of word lengths for words longer than 3 characters.

Matplotlib

words = ['apple', 'bat', 'carrot', 'dog']
lengths = {word: [1] for word in words if len(word) [2] 3}

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Alen(word)

B>

C<

Dword

Attempts:

3 left

💡 Hint

Common Mistakes

Using < instead of > filters the wrong words.

Using the word itself instead of its length as the value.

The dictionary comprehension maps each word to its length only if the word length is greater than 3.

5fill in blank

hard

Fill all three blanks to create a dictionary of uppercase words mapped to their lengths if length is greater than 3.

Matplotlib

words = ['apple', 'bat', 'carrot', 'dog']
result = { [1]: [2] for word in words if len(word) [3] 3 }

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Aword.upper()

Blen(word)

C>

Dword

Attempts:

3 left

💡 Hint

Common Mistakes

Using the original word instead of uppercase as key.

Using < instead of > in the condition.

This dictionary comprehension creates keys as uppercase words and values as their lengths, only for words longer than 3 characters.

Practice

1. What does the width parameter control in a matplotlib bar chart?

easy

A. The thickness of each bar

B. The color of each bar

C. The height of each bar

D. The label of each bar

Solution

1. Step 1: Understand the width parameter

   The width parameter in matplotlib's bar chart sets how wide or thick each bar appears on the x-axis.

2. Step 2: Differentiate from other properties

   Color, height, and label are controlled by other parameters, not width.

3. Final Answer:

   The thickness of each bar -> Option A

4. Quick Check:

   Bar width = thickness [OK]

Hint: Width changes bar thickness, not height or color [OK]

Common Mistakes:

• Confusing width with height
• Thinking width changes bar color
• Assuming width changes bar labels

2. Which of the following is the correct way to set the bar width to 0.5 in matplotlib?

easy

A. plt.bar(x, height, thickness=0.5)

B. plt.bar(x, height, width=0.5)

C. plt.bar(x, height, size=0.5)

D. plt.bar(x, height, length=0.5)

Solution

1. Step 1: Recall matplotlib bar syntax

   The plt.bar() function uses the width parameter to set bar thickness.

2. Step 2: Identify correct parameter name

   Only width is valid; size, thickness, and length are invalid for bar width.

3. Final Answer:

   plt.bar(x, height, width=0.5) -> Option B

4. Quick Check:

   Use width to set bar thickness [OK]

Hint: Use 'width' parameter to set bar thickness [OK]

Common Mistakes:

• Using 'size' instead of 'width'
• Using 'thickness' or 'length' which are invalid
• Omitting the width parameter

3. What will be the x positions of bars when running this code?

import matplotlib.pyplot as plt
x = [1, 2, 3]
heights = [4, 5, 6]
plt.bar([pos + 0.2 for pos in x], heights, width=0.4)
plt.show()

medium

A. [1, 2, 3]

B. [0.4, 1.4, 2.4]

C. [1.2, 2.2, 3.2]

D. [0.8, 1.8, 2.8]

Solution

1. Step 1: Analyze the x positions

   The code shifts each x position by adding 0.2, so positions become [1+0.2, 2+0.2, 3+0.2] = [1.2, 2.2, 3.2].

2. Step 2: Understand bar width effect

   The width=0.4 sets bar thickness but does not change the center positions.

3. Final Answer:

   [1.2, 2.2, 3.2] -> Option C

4. Quick Check:

   Positions shifted by 0.2 = [1.2, 2.2, 3.2] [OK]

Hint: Add offset to x list to shift bar positions [OK]

Common Mistakes:

• Ignoring the +0.2 shift
• Confusing width with position shift
• Assuming bars stay at original x

4. Identify the error in this code that tries to plot two sets of bars side by side:

import matplotlib.pyplot as plt
x = [1, 2, 3]
heights1 = [4, 5, 6]
heights2 = [7, 8, 9]
plt.bar(x, heights1, width=0.5)
plt.bar(x, heights2, width=0.5)
plt.show()

medium

A. Bars overlap because positions are the same

B. Width parameter is invalid

C. Heights lists have different lengths

D. Missing plt.show() call

Solution

1. Step 1: Check bar positions

   Both bar sets use the same x positions, so bars overlap on the plot.

2. Step 2: Confirm width and data lengths

   Width=0.5 is valid, heights lists have same length, and plt.show() is present.

3. Final Answer:

   Bars overlap because positions are the same -> Option A

4. Quick Check:

   Same x positions cause overlap [OK]

Hint: Shift x positions to avoid bar overlap [OK]

Common Mistakes:

• Not shifting x for multiple bar sets
• Thinking width causes overlap
• Ignoring plt.show() call

5. You want to plot three groups of bars side by side for categories 1, 2, 3. Each group has 3 bars. Which code correctly positions bars to avoid overlap?

import matplotlib.pyplot as plt
x = [1, 2, 3]
heights_a = [3, 5, 7]
heights_b = [4, 6, 8]
heights_c = [2, 4, 6]
width = 0.2
plt.bar([p - width for p in x], heights_a, width=width)
plt.bar(x, heights_b, width=width)
plt.bar([p + width for p in x], heights_c, width=width)
plt.show()

hard

A. Incorrect: width parameter missing

B. Incorrect: bars overlap because width is too large

C. Incorrect: bars all plotted at same x positions

D. Correct: bars shifted left, center, right by width

Solution

1. Step 1: Analyze bar positions

   Bars for group A are shifted left by width, group B at center, group C shifted right by width, so bars are side by side without overlap.

2. Step 2: Check width and spacing

   Width=0.2 is small enough to fit three bars side by side within each category.

3. Final Answer:

   Correct: bars shifted left, center, right by width -> Option D

4. Quick Check:

   Shift bars by ±width to avoid overlap [OK]

Hint: Shift bars by ±width to place side by side [OK]

Common Mistakes:

• Not shifting bars, causing overlap
• Using width too large for spacing
• Forgetting to set width parameter