Heatmap with plt.pcolormesh in Matplotlib - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a heatmap using plt.pcolormesh.

Matplotlib

import matplotlib.pyplot as plt
import numpy as np

data = np.array([[1, 2], [3, 4]])
plt.[1](data)
plt.show()

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

Aplot

Bscatter

Cpcolormesh

Dbar

Attempts:

3 left

💡 Hint

Common Mistakes

Using plt.plot instead of plt.pcolormesh.

Using plt.scatter which is for scatter plots.

Using plt.bar which is for bar charts.

The plt.pcolormesh function creates a heatmap from a 2D array.

2fill in blank

medium

Complete the code to add a colorbar to the heatmap.

Matplotlib

import matplotlib.pyplot as plt
import numpy as np

data = np.array([[5, 10], [15, 20]])
mesh = plt.pcolormesh(data)
plt.[1]()
plt.show()

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

Acolorbar

Blegend

Cgrid

Dtitle

Attempts:

3 left

💡 Hint

Common Mistakes

Using plt.legend which is for plot legends.

Using plt.grid which adds grid lines.

Using plt.title which adds a title.

The plt.colorbar() function adds a color scale bar to the heatmap.

3fill in blank

hard

Fix the error in the code to correctly display the heatmap with a custom colormap.

Matplotlib

import matplotlib.pyplot as plt
import numpy as np

data = np.array([[1, 4], [9, 16]])
plt.pcolormesh(data, cmap=[1])
plt.colorbar()
plt.show()

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

ANone

Bviridis

C'blue'

D'viridis'

Attempts:

3 left

💡 Hint

Common Mistakes

Passing the colormap name without quotes causes an error.

Using an invalid colormap name.

Passing None disables the colormap.

The cmap parameter expects a string name of the colormap in quotes.

4fill in blank

hard

Fill both blanks to create a heatmap with labeled axes and a title.

Matplotlib

import matplotlib.pyplot as plt
import numpy as np

data = np.array([[2, 3], [4, 5]])
plt.pcolormesh(data)
plt.xlabel([1])
plt.title([2])
plt.colorbar()
plt.show()

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

A'X axis'

B'Y axis'

C'My Heatmap'

D'Data Values'

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping axis labels and title text.

Forgetting to put labels in quotes.

Not adding a title at all.

Use plt.xlabel to label the x-axis and plt.title to add a title to the plot.

5fill in blank

hard

Fill all three blanks to create a heatmap with custom x and y ticks and a colorbar label.

Matplotlib

import matplotlib.pyplot as plt
import numpy as np

data = np.array([[7, 8], [9, 10]])
mesh = plt.pcolormesh(data)
plt.xticks([1])
plt.yticks([2])
plt.colorbar(mesh, label=[3])
plt.show()

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

A[0, 1]

C'Intensity'

D[1, 2]

Attempts:

3 left

💡 Hint

Common Mistakes

Using strings instead of lists for ticks.

Not passing the mesh object to colorbar.

Forgetting quotes around the label.

Use plt.xticks and plt.yticks to set tick positions. The colorbar label is a string describing the data.

Practice

1. What does plt.pcolormesh do in matplotlib?

easy

A. It creates a scatter plot with colored dots.

B. It plots a line graph connecting points.

C. It creates a heatmap by coloring a grid based on data values.

D. It draws bar charts with colored bars.

Solution

1. Step 1: Understand the function purpose

   plt.pcolormesh colors a grid of cells based on the values in a 2D array, making a heatmap.

2. Step 2: Compare with other plot types

   Line graphs connect points, scatter plots show dots, and bar charts show bars, none of which match pcolormesh.

3. Final Answer:

   It creates a heatmap by coloring a grid based on data values. -> Option C

4. Quick Check:

   Heatmap = pcolormesh = A [OK]

Hint: pcolormesh colors grids for heatmaps, not lines or bars [OK]

Common Mistakes:

• Confusing pcolormesh with line or scatter plots
• Thinking pcolormesh plots points instead of colored cells
• Assuming pcolormesh creates bar charts

2. Which of these is the correct way to add a colorbar to a heatmap created with plt.pcolormesh?

easy

A. plt.colorbar()

B. plt.add_colorbar()

C. plt.show_colorbar()

D. plt.colorbar_add()

Solution

1. Step 1: Recall matplotlib colorbar syntax

   The correct function to add a colorbar is plt.colorbar().

2. Step 2: Check other options

   Functions like plt.add_colorbar(), plt.show_colorbar(), or plt.colorbar_add() do not exist in matplotlib.

3. Final Answer:

   plt.colorbar() -> Option A

4. Quick Check:

   Colorbar function = plt.colorbar() = B [OK]

Hint: Use plt.colorbar() exactly to add color legend [OK]

Common Mistakes:

• Using non-existent functions like plt.add_colorbar()
• Forgetting to add a colorbar after pcolormesh
• Trying to add colorbar before plotting heatmap

3. What will the following code display?

import matplotlib.pyplot as plt
import numpy as np

Z = np.array([[1, 2], [3, 4]])
plt.pcolormesh(Z)
plt.colorbar()
plt.show()

medium

A. An error because Z is not a 1D array.

B. A line plot connecting points 1, 2, 3, 4.

C. A scatter plot with 4 points colored by values.

D. A 2x2 heatmap with colors representing values 1 to 4 and a colorbar.

Solution

1. Step 1: Understand the input array Z

   Z is a 2x2 numpy array with values from 1 to 4.

2. Step 2: What does plt.pcolormesh(Z) do?

   It creates a heatmap grid colored by the values in Z, so 4 colored squares.

3. Step 3: Adding plt.colorbar()

   This adds a color scale legend showing how colors map to values 1 to 4.

4. Final Answer:

   A 2x2 heatmap with colors representing values 1 to 4 and a colorbar. -> Option D

5. Quick Check:

   2x2 heatmap + colorbar = C [OK]

Hint: pcolormesh with 2D array shows colored grid matching array shape [OK]

Common Mistakes:

• Thinking pcolormesh needs 1D array only
• Confusing heatmap with line or scatter plots
• Forgetting colorbar shows value-color mapping

4. Identify the error in this code snippet:

import matplotlib.pyplot as plt
import numpy as np

Z = np.array([[1, 2], [3, 4]])
plt.pcolormesh(Z)
plt.colorbar
plt.show()

medium

A. Missing parentheses after plt.colorbar causing no colorbar to show.

B. Z should be a 1D array, not 2D.

C. plt.show() must come before plt.pcolormesh().

D. plt.pcolormesh() requires x and y coordinates explicitly.

Solution

1. Step 1: Check plt.colorbar usage

   The code uses plt.colorbar without parentheses, so the function is not called.

2. Step 2: Effect of missing parentheses

   Without calling the function, no colorbar appears on the plot.

3. Final Answer:

   Missing parentheses after plt.colorbar causing no colorbar to show. -> Option A

4. Quick Check:

   Call plt.colorbar() with () to show colorbar [OK]

Hint: Always add () after plt.colorbar to display it [OK]

Common Mistakes:

• Forgetting () after plt.colorbar
• Thinking 2D array is invalid input
• Calling plt.show() too early
• Assuming x,y needed for simple heatmap

5. You want to create a heatmap of a 3x3 matrix with values from 0 to 8 using plt.pcolormesh. Which code correctly sets the x and y axis labels to 'X Axis' and 'Y Axis' and adds a colorbar?

hard

A. import matplotlib.pyplot as plt
import numpy as np
Z = np.arange(9).reshape(3,3)
plt.pcolormesh(Z)
plt.set_xlabel('X Axis')
plt.set_ylabel('Y Axis')
plt.colorbar()
plt.show()

B. import matplotlib.pyplot as plt
import numpy as np
Z = np.arange(9).reshape(3,3)
plt.pcolormesh(Z)
plt.xlabel('X Axis')
plt.ylabel('Y Axis')
plt.colorbar()
plt.show()

C. import matplotlib.pyplot as plt
import numpy as np
Z = np.arange(9).reshape(3,3)
plt.pcolormesh(Z)
plt.xlabel = 'X Axis'
plt.ylabel = 'Y Axis'
plt.colorbar()
plt.show()

D. import matplotlib.pyplot as plt
import numpy as np
Z = np.arange(9).reshape(3,3)
plt.pcolormesh(Z)
plt.axis_labels('X Axis', 'Y Axis')
plt.colorbar()
plt.show()

Solution

1. Step 1: Check axis label functions

   The correct functions to label axes are plt.xlabel() and plt.ylabel().

2. Step 2: Verify colorbar and show usage

   plt.colorbar() must be called with parentheses, and plt.show() displays the plot.

3. Step 3: Identify incorrect options

   import matplotlib.pyplot as plt import numpy as np Z = np.arange(9).reshape(3,3) plt.pcolormesh(Z) plt.set_xlabel('X Axis') plt.set_ylabel('Y Axis') plt.colorbar() plt.show() uses non-existent plt.set_xlabel(), C assigns strings instead of calling functions, D uses a non-existent plt.axis_labels().

4. Final Answer:

   import matplotlib.pyplot as plt import numpy as np Z = np.arange(9).reshape(3,3) plt.pcolormesh(Z) plt.xlabel('X Axis') plt.ylabel('Y Axis') plt.colorbar() plt.show() -> Option B

5. Quick Check:

   Use plt.xlabel(), plt.ylabel(), plt.colorbar() [OK]

Hint: Use plt.xlabel() and plt.ylabel() to label axes [OK]

Common Mistakes:

• Using plt.set_xlabel() instead of plt.xlabel()
• Assigning labels instead of calling functions
• Forgetting parentheses on plt.colorbar()
• Using non-existent axis_labels() function