3D bar charts in Matplotlib - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the 3D plotting toolkit from matplotlib.

Matplotlib

from mpl_toolkits.mplot3d import [1]

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

Aplot3d

BAxes3D

Cbar3d

Dfigure3d

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to import plot3d instead of Axes3D.

Using bar3d which is a method, not a class.

Importing figure3d which does not exist.

The Axes3D class is needed to create 3D plots in matplotlib.

2fill in blank

medium

Complete the code to create a 3D axes object from a matplotlib figure.

Matplotlib

fig = plt.figure()
ax = fig.add_subplot(111, projection=[1])

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

A'2d'

B'xyz'

C'3D'

D'3d'

Attempts:

3 left

💡 Hint

Common Mistakes

Using uppercase '3D' instead of lowercase '3d'.

Using '2d' which creates a 2D plot.

Using 'xyz' which is not a valid projection.

To create a 3D plot, the projection must be set to '3d' (all lowercase).

3fill in blank

hard

Fix the error in the code to plot a 3D bar chart with correct bar widths.

Matplotlib

ax.bar3d(x, y, z, [1], dy, dz, color='blue')

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

Adx

Bx

Cwidth

Dheight

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'x' instead of 'dx' for width.

Using 'width' or 'height' which are not parameter names.

Confusing dy and dz with dx.

The bar3d method requires dx as the width of bars along the x-axis.

4fill in blank

hard

Fill both blanks to create a dictionary comprehension that maps each word to its length if length is greater than 3.

Matplotlib

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

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

Alen(word)

Blen(word) > 3

Cword > 3

Dlen(words) > 3

Attempts:

3 left

💡 Hint

Common Mistakes

Using word > 3 which compares a string to a number.

Using len(words) > 3 which checks the whole list length.

Putting the condition in the wrong place.

The dictionary maps each word to its length using len(word). The condition checks if the length is greater than 3 with len(word) > 3.

5fill in blank

hard

Fill all three blanks to create a dictionary comprehension that maps uppercase words to their counts if count is greater than 1.

Matplotlib

result = [1]: [2] for [3], [2] in data.items() if [2] > 1

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

Aword.upper()

Bcount

Cword

Ddata

Attempts:

3 left

💡 Hint

Common Mistakes

Using data instead of word in the loop.

Using word instead of count in the value.

Not filtering counts greater than 1.

The comprehension maps the uppercase version of each word (word.upper()) to its count (count) for word, count in data.items() if the count is greater than 1.

Practice

1. What does a 3D bar chart in matplotlib primarily represent?

easy

A. Data with two position dimensions and one height dimension

B. Only two-dimensional data with color coding

C. A line graph with three lines

D. A pie chart with depth effect

Solution

1. Step 1: Understand the axes in 3D bar charts

   3D bar charts use two axes for position (x and y) and one axis for height (z).

2. Step 2: Identify the data representation

   The height of each bar shows the value, while the base position shows categories or coordinates.

3. Final Answer:

   Data with two position dimensions and one height dimension -> Option A

4. Quick Check:

   3D bar chart = 2D position + height [OK]

Hint: Remember: 3D bars have x, y positions and z height [OK]

Common Mistakes:

• Confusing 3D bars with 2D bar charts
• Thinking 3D bars only show color differences
• Assuming 3D bars are line graphs

2. Which of the following is the correct way to create 3D axes in matplotlib before plotting a 3D bar chart?

easy

A. ax = plt.axes3d()

B. ax = plt.subplots(projection='3d')

C. ax = plt.subplot(projection='3d')

D. ax = plt.figure().add_subplot(111, projection='3d')

Solution

1. Step 1: Recall how to create 3D axes in matplotlib

   The common method is to create a figure and add a 3D subplot using add_subplot(111, projection='3d').

2. Step 2: Check each option

   ax = plt.subplot(projection='3d') uses subplot instead of add_subplot, which is incorrect. ax = plt.subplots(projection='3d') returns a tuple (figure, axes), so assigning directly to ax is incorrect. ax = plt.axes3d() is not a valid matplotlib function.

3. Final Answer:

   ax = plt.figure().add_subplot(111, projection='3d') -> Option D

4. Quick Check:

   Use figure().add_subplot with projection='3d' [OK]

Hint: Use figure().add_subplot(111, projection='3d') to get 3D axes [OK]

Common Mistakes:

• Using plt.subplot instead of plt.figure().add_subplot
• Trying to call non-existent plt.axes3d()
• Confusing subplots() with subplot()

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

import matplotlib.pyplot as plt
from mpl_toolkits.mplot3d import Axes3D
fig = plt.figure()
ax = fig.add_subplot(111, projection='3d')
x = [1, 2]
y = [3, 4]
z = [0, 0]
dx = dy = dz = [1, 1]
ax.bar3d(x, y, z, dx, dy, dz, color='red')
plt.show()

medium

A. Two red bars at positions (1,3) and (2,4) with height 1

B. Two red bars at positions (0,0) and (1,1) with height 1

C. Error because dx, dy, dz should be scalars, not lists

D. Empty plot with no bars

Solution

1. Step 1: Understand the parameters of ax.bar3d

   Parameters x, y, z are the positions of bars. dx, dy, dz are the sizes along each axis. Here, x=[1,2], y=[3,4], z=[0,0], and dx=dy=dz=[1,1].

2. Step 2: Analyze the plot output

   Two bars will appear at (1,3,0) and (2,4,0) with width=1, depth=1, height=1, colored red.

3. Final Answer:

   Two red bars at positions (1,3) and (2,4) with height 1 -> Option A

4. Quick Check:

   Positions and sizes match bars at (1,3) and (2,4) [OK]

Hint: Check x,y,z positions and dx,dy,dz sizes carefully [OK]

Common Mistakes:

• Assuming dx, dy, dz must be scalars only
• Confusing bar positions with sizes
• Expecting bars at (0,0) instead of given x,y

4. Identify the error in this code for plotting a 3D bar chart:

import matplotlib.pyplot as plt
fig = plt.figure()
ax = fig.add_subplot(111, projection='3d')
x = [1, 2, 3]
y = [4, 5]
z = [0, 0, 0]
dx = dy = dz = 1
ax.bar3d(x, y, z, dx, dy, dz)
plt.show()

medium

A. Missing import for Axes3D

B. Length of y does not match length of x and z

C. dx, dy, dz must be lists, not scalars

D. ax.bar3d does not accept scalar sizes

Solution

1. Step 1: Check lengths of position arrays

   x has length 3, y has length 2, z has length 3. They must all be the same length for bar3d.

2. Step 2: Verify size parameters

   dx, dy, dz can be scalars or lists matching length of bars, so scalars are allowed.

3. Final Answer:

   Length of y does not match length of x and z -> Option B

4. Quick Check:

   All position arrays must have equal length [OK]

Hint: Check all position lists have same length [OK]

Common Mistakes:

• Assuming dx, dy, dz must be lists
• Ignoring mismatch in array lengths
• Forgetting to import mpl_toolkits.mplot3d (not needed here)

5. You want to plot a 3D bar chart showing sales data for 3 products over 4 months. Which approach correctly sets up the data for ax.bar3d()?

hard

A. Use x, y, z all as sales values, dz as zeros

B. Use x as months, y as products, z as sales values, and dz as ones

C. Use x as product indices repeated for each month, y as month indices tiled for each product, z as zeros, and dz as sales values

D. Use x and y as sales values, z as product indices, dz as month indices

Solution

1. Step 1: Understand the data layout for 3D bars

   x and y represent positions (product and month), z is the base height (usually zero), dz is the height of bars (sales values).

2. Step 2: Arrange data correctly

   Repeat product indices for each month (x), tile month indices for each product (y), set z to zero, and use sales data as dz.

3. Final Answer:

   Use x as product indices repeated for each month, y as month indices tiled for each product, z as zeros, and dz as sales values -> Option C

4. Quick Check:

   Positions = product/month, height = sales [OK]

Hint: Map x,y to categories, dz to values for bar height [OK]

Common Mistakes:

• Mixing sales values as positions instead of heights
• Using z as sales height instead of dz
• Not repeating/tiling indices properly for grid