3D bar charts in Matplotlib - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of 3D Bar Chart Data Arrays

What is the output of the following code snippet that prepares data for a 3D bar chart?

Matplotlib

import numpy as np
x = np.arange(3)
y = np.arange(2)
xpos, ypos = np.meshgrid(x, y)
xpos = xpos.flatten()
ypos = ypos.flatten()
zpos = np.zeros_like(xpos)
print(xpos, ypos, zpos)

A [0 1 2 0 1 2] [0 0 0 1 1 1] [0 0 0 0 0 0]

B [0 0 1 1 2 2] [0 1 0 1 0 1] [0 0 0 0 0 0]

C [0 1 2] [0 1] [0 0 0]

D [0 1 2 0 1 2] [0 1 0 1 0 1] [0 0 0 0 0 0]

💡 Hint

Think about how meshgrid arranges coordinates and what flatten() does.

np.meshgrid creates coordinate matrices from coordinate vectors. Flattening these matrices gives arrays of x and y positions for bars. zpos is zeros because bars start from zero height.

❓ data_output

intermediate

Number of Bars in 3D Bar Chart

Given x = range(4) and y = range(3), how many bars will be drawn in a 3D bar chart created by plotting all combinations of x and y?

A 7

B 9

C 6

D 12

💡 Hint

Multiply the number of x positions by the number of y positions.

Each x value pairs with each y value, so total bars = 4 * 3 = 12.

❓ visualization

advanced

Identify the Correct 3D Bar Chart Plot

Which option shows the correct 3D bar chart plot code that creates bars with heights from the list [1, 3, 2, 5] at positions (0,0), (1,0), (0,1), and (1,1)?

A ax.bar3d([0,1,0,1], [0,0,1,1], [0,0,0,0], 1, 1, [1,3,2,5])

B ax.bar3d([0,1,0,1], [0,0,1,1], [0,0,0,0], [1,1,1,1], [1,1,1,1], [1,3,2,5])

C ax.bar3d([0,1,0,1], [0,0,1,1], [1,3,2,5], 1, 1, 0)

D ax.bar3d([0,0,1,1], [0,1,0,1], [0,0,0,0], 1, 1, [1,3,2,5])

💡 Hint

Check the order and length of parameters for bar3d: xpos, ypos, zpos, dx, dy, dz.

bar3d requires arrays for x, y, z positions, widths dx, dy, and heights dz. Option B correctly provides all six parameters with matching lengths.

🔧 Debug

advanced

Error in 3D Bar Chart Plotting Code

What error will this code raise? import matplotlib.pyplot as plt from mpl_toolkits.mplot3d import Axes3D fig = plt.figure() ax = fig.add_subplot(111, projection='3d') x = [0,1] y = [0,1] z = [0,0] dx = dy = dz = [1,2] ax.bar3d(x, y, z, dx, dy, dz) plt.show()

Matplotlib

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

A TypeError: 'int' object is not iterable

B TypeError: bar3d() missing 3 required positional arguments

C ValueError: setting an array element with a sequence

D No error, plot displays correctly

💡 Hint

Check how dx, dy, dz are assigned and their types.

dx = dy = dz = [1,2] assigns the same list to all three variables. This causes bar3d to receive lists where it expects numbers or arrays of matching shape, leading to a ValueError.

🚀 Application

expert

Calculate Total Volume of Bars in 3D Bar Chart

Given the following data for a 3D bar chart: x = [0, 1, 2] y = [0, 1] dz = [2, 3, 1, 4, 2, 5] Each bar has width dx=1 and depth dy=1. What is the total volume of all bars combined?

A 17

B 18

C 19

D 20

💡 Hint

Volume of each bar = dx * dy * dz. Sum all volumes.

Each bar volume is 1 * 1 * dz value. Sum dz values: 2+3+1+4+2+5 = 17. Since dx and dy are 1, total volume = 17.