Error bars on bar charts in Matplotlib - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the matplotlib.pyplot module as plt.

Matplotlib

import [1] as plt

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

Anumpy

Bpandas

Cmatplotlib.pyplot

Dseaborn

Attempts:

3 left

💡 Hint

Common Mistakes

Importing the wrong module like numpy or pandas.

Forgetting to use 'as plt' alias.

We import matplotlib.pyplot as plt to create plots.

2fill in blank

medium

Complete the code to create a bar chart with error bars using plt.bar.

Matplotlib

plt.bar(x, height, yerr=[1])

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

Ax

Berrors

Cheight

Dwidth

Attempts:

3 left

💡 Hint

Common Mistakes

Passing the wrong variable like x or height to yerr.

Not passing any error values.

The yerr parameter takes the error values to show error bars.

3fill in blank

hard

Fix the error in the code to correctly display error bars on the bar chart.

Matplotlib

plt.bar(x, height, yerr=[1], capsize=5)
plt.show()

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

Aerror

Berr

Cerror_bars

Derrors

Attempts:

3 left

💡 Hint

Common Mistakes

Using a variable name that does not exist.

Typos in the error variable name.

The variable holding error values is named errors. Using the correct variable name fixes the error.

4fill in blank

hard

Fill both blanks to create a dictionary comprehension that maps words to their lengths only if length is greater than 3.

Matplotlib

{word: [1] for word in words if [2]

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

Alen(word)

Blen(word) > 3

Cword

Dword > 3

Attempts:

3 left

💡 Hint

Common Mistakes

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

Incorrect condition syntax.

The dictionary maps each word to its length using len(word). The condition keeps words longer than 3 characters.

5fill in blank

hard

Fill all three blanks to create a dictionary comprehension that maps uppercase words to their counts only if count is greater than 0.

Matplotlib

{ [1]: [2] for [3], count in data.items() if count > 0 }

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

Aword.upper()

Bcount

Cword

Dcount.upper()

Attempts:

3 left

💡 Hint

Common Mistakes

Using count.upper() which is invalid since count is a number.

Swapping keys and values.

The keys are uppercase words using word.upper(). The values are counts. The loop variable is word.

Practice

1. What does the yerr parameter do when creating a bar chart in matplotlib?

easy

A. It changes the color of the bars.

B. It sets the width of the bars.

C. It adds vertical error bars to each bar showing uncertainty.

D. It adds labels to the bars.

Solution

1. Step 1: Understand the role of yerr

   The yerr parameter in matplotlib bar charts specifies the size of vertical error bars to show uncertainty or variation.

2. Step 2: Compare with other options

   Other options like color, width, or labels are controlled by different parameters, not yerr.

3. Final Answer:

   It adds vertical error bars to each bar showing uncertainty. -> Option C

4. Quick Check:

   yerr = vertical error bars [OK]

Hint: Remember: yerr means vertical error bars [OK]

Common Mistakes:

• Confusing yerr with bar width
• Thinking yerr changes bar color
• Assuming yerr adds labels

2. Which of the following is the correct syntax to add error bars with size 0.2 to a bar chart using matplotlib?

easy

A. plt.bar(x, height, err=0.2)

B. plt.bar(x, height, error=0.2)

C. plt.bar(x, height, yerror=0.2)

D. plt.bar(x, height, yerr=0.2)

Solution

1. Step 1: Recall the correct parameter name

   The correct parameter to add vertical error bars in matplotlib bar charts is yerr.

2. Step 2: Check the syntax

   The syntax plt.bar(x, height, yerr=0.2) correctly adds error bars of size 0.2.

3. Final Answer:

   plt.bar(x, height, yerr=0.2) -> Option D

4. Quick Check:

   Correct parameter is yerr [OK]

Hint: Use exact parameter name yerr for error bars [OK]

Common Mistakes:

• Using wrong parameter names like error or err
• Misspelling yerr as yerror
• Forgetting to assign a value to yerr

3. What will be the output of this code snippet?

import matplotlib.pyplot as plt
x = [1, 2, 3]
heights = [3, 5, 2]
errors = [0.5, 0.2, 0.3]
plt.bar(x, heights, yerr=errors, capsize=5)
plt.show()

medium

A. A syntax error because capsize is not a valid parameter.

B. A bar chart with bars at x=1,2,3 with heights 3,5,2 and vertical error bars with caps of length 5.

C. A bar chart with bars but no error bars visible.

D. A bar chart with horizontal error bars.

Solution

1. Step 1: Understand the code

   The code creates bars at positions 1, 2, 3 with heights 3, 5, 2 respectively and adds vertical error bars sized by the list errors.

2. Step 2: Role of capsize

   The capsize=5 parameter adds horizontal caps at the ends of error bars, making them visible and 5 points long.

3. Final Answer:

   A bar chart with bars at x=1,2,3 with heights 3,5,2 and vertical error bars with caps of length 5. -> Option B

4. Quick Check:

   yerr + capsize = vertical error bars with caps [OK]

Hint: capsize adds visible ends to error bars [OK]

Common Mistakes:

• Thinking capsize disables error bars
• Confusing vertical and horizontal error bars
• Assuming capsize causes syntax error

4. Identify the error in this code that tries to add error bars to a bar chart:

import matplotlib.pyplot as plt
x = [1, 2, 3]
heights = [4, 6, 5]
errors = [0.3, 0.4, 0.2]
plt.bar(x, heights, yerror=errors)
plt.show()

medium

A. The parameter name should be yerr, not yerror.

B. The errors list length does not match heights length.

C. plt.bar does not support error bars.

D. The x values must be strings, not integers.

Solution

1. Step 1: Check parameter names

   The parameter to add vertical error bars is yerr, not yerror.

2. Step 2: Validate other parts

   The lengths of errors and heights match, and plt.bar supports error bars with yerr.

3. Final Answer:

   The parameter name should be yerr, not yerror. -> Option A

4. Quick Check:

   Correct parameter is yerr, not yerror [OK]

Hint: Use exact parameter yerr, spelling matters [OK]

Common Mistakes:

• Using yerror instead of yerr
• Ignoring parameter name case sensitivity
• Assuming plt.bar can't have error bars

5. You want to create a bar chart with 4 bars and different error sizes for each bar. Which code correctly achieves this with visible error bar caps?

hard

A. plt.bar([1,2,3,4], [5,7,3,4], yerr=[0.2,0.3,0.1,0.4], capsize=3)

B. plt.bar([1,2,3,4], [5,7,3,4], yerr=0.3, capsize=0)

C. plt.bar([1,2,3,4], [5,7,3,4], yerr=[0.2,0.3], capsize=3)

D. plt.bar([1,2,3,4], [5,7,3,4], error=[0.2,0.3,0.1,0.4], capsize=3)

Solution

1. Step 1: Check error bar sizes match bars

   There are 4 bars, so the yerr list must have 4 values. plt.bar([1,2,3,4], [5,7,3,4], yerr=[0.2,0.3,0.1,0.4], capsize=3) has 4 error sizes matching bars.

2. Step 2: Verify capsize for visible caps

   plt.bar([1,2,3,4], [5,7,3,4], yerr=[0.2,0.3,0.1,0.4], capsize=3) uses capsize=3 which makes error bar caps visible. Other options fail: one uses a single yerr value with capsize=0 (no caps), another provides only two error sizes (mismatch), and one uses wrong parameter error.

3. Final Answer:

   plt.bar([1,2,3,4], [5,7,3,4], yerr=[0.2,0.3,0.1,0.4], capsize=3) -> Option A

4. Quick Check:

   yerr list length = bars count + capsize > 0 [OK]

Hint: Match yerr length to bars and set capsize > 0 [OK]

Common Mistakes:

• Using single yerr value for multiple bars
• Setting capsize to zero hides caps
• Using wrong parameter name error instead of yerr