0
0
Matplotlibdata~10 mins

Grouped bar charts in Matplotlib - Step-by-Step Execution

Choose your learning style9 modes available
Concept Flow - Grouped bar charts
Prepare data for groups and categories
Calculate bar positions for each group
Plot bars side-by-side for each category
Add labels, title, legend
Display the grouped bar chart
Grouped bar charts show multiple bars side-by-side for each group, allowing easy comparison across categories.
Execution Sample
Matplotlib
import matplotlib.pyplot as plt

labels = ['A', 'B', 'C']
values1 = [5, 7, 3]
values2 = [6, 8, 4]

x = range(len(labels))

plt.bar([p - 0.2 for p in x], values1, width=0.4, label='Set 1')
plt.bar([p + 0.2 for p in x], values2, width=0.4, label='Set 2')

plt.xticks(x, labels)
plt.legend()
plt.show()
This code plots two sets of bars side-by-side for each label, creating a grouped bar chart.
Execution Table
StepActionVariable/ValueEffect/Output
1Define labelslabels = ['A', 'B', 'C']Labels for x-axis groups set
2Define values1values1 = [5, 7, 3]First data set values stored
3Define values2values2 = [6, 8, 4]Second data set values stored
4Calculate x positionsx = range(3)x = [0,1,2], positions for groups
5Calculate positions for bars set 1[p - 0.2 for p in x]Positions: [-0.2, 0.8, 1.8] for first bars
6Plot bars set 1plt.bar([p - 0.2 for p in x], values1, width=0.4, label='Set 1')Bars for Set 1 drawn at shifted left positions
7Calculate positions for bars set 2[p + 0.2 for p in x]Positions: [0.2, 1.2, 2.2] for second bars
8Plot bars set 2plt.bar([p + 0.2 for p in x], values2, width=0.4, label='Set 2')Bars for Set 2 drawn at shifted right positions
9Set x-axis ticksplt.xticks(x, labels)Labels 'A','B','C' shown under groups
10Add legendplt.legend()Legend shows 'Set 1' and 'Set 2' labels
11Show plotplt.show()Grouped bar chart displayed
12End-Execution complete
💡 All bars plotted and chart displayed, execution ends.
Variable Tracker
VariableStartAfter Step 4After Step 5After Step 7Final
labelsundefined['A', 'B', 'C']['A', 'B', 'C']['A', 'B', 'C']['A', 'B', 'C']
values1undefined[5, 7, 3][5, 7, 3][5, 7, 3][5, 7, 3]
values2undefined[6, 8, 4][6, 8, 4][6, 8, 4][6, 8, 4]
xundefined[0, 1, 2][0, 1, 2][0, 1, 2][0, 1, 2]
positions set 1undefinedundefined[-0.2, 0.8, 1.8][-0.2, 0.8, 1.8][-0.2, 0.8, 1.8]
positions set 2undefinedundefinedundefined[0.2, 1.2, 2.2][0.2, 1.2, 2.2]
Key Moments - 3 Insights
Why do we subtract and add 0.2 to the x positions for the two sets of bars?
Subtracting 0.2 shifts the first set of bars slightly left, and adding 0.2 shifts the second set right, so bars don't overlap and appear side-by-side as shown in steps 5 and 7.
What does plt.xticks(x, labels) do in the grouped bar chart?
It sets the x-axis ticks at positions x = [0,1,2] and labels them with 'A', 'B', 'C' so viewers know which group each pair of bars belongs to, as in step 9.
Why do we use the same width (0.4) for both sets of bars?
Using the same width ensures bars are uniform in size and fit neatly side-by-side without overlapping, as seen in steps 6 and 8.
Visual Quiz - 3 Questions
Test your understanding
Look at the execution table at step 5. What are the positions for the first set of bars?
A[-0.2, 0.8, 1.8]
B[0, 1, 2]
C[0.2, 1.2, 2.2]
D[0.4, 1.4, 2.4]
💡 Hint
Check the 'Variable/Value' column at step 5 in the execution_table.
At which step are the x-axis labels 'A', 'B', 'C' set under the bars?
AStep 6
BStep 7
CStep 9
DStep 10
💡 Hint
Look for plt.xticks call in the execution_table.
If we increase the bar width to 0.8 for both sets, what will likely happen?
ABars will disappear
BBars will overlap because total width exceeds group spacing
CBars will be thinner and spaced out
DBars will be colored differently
💡 Hint
Consider the width and position shifts in steps 5, 6, 7, and 8.
Concept Snapshot
Grouped bar charts show multiple bars side-by-side for each group.
Use position shifts (e.g., -0.2, +0.2) to separate bars.
Set bar width to fit bars neatly without overlap.
Use plt.xticks to label groups on x-axis.
Add legend to identify each data set.
Call plt.show() to display the chart.
Full Transcript
This visual execution traces how to create grouped bar charts using matplotlib. We start by defining labels and two sets of values. We calculate x positions for groups and shift them left and right to place bars side-by-side. Bars are plotted with the same width to avoid overlap. The x-axis ticks are set to show group labels, and a legend is added to distinguish data sets. Finally, the chart is displayed. Key points include shifting bar positions to group them and setting x-axis labels for clarity.