Multiple time series comparison in Matplotlib - Step-by-Step Execution

Concept Flow - Multiple time series comparison

Load data for series A

↓

Load data for series B

↓

Prepare time axis

↓

Plot series A on graph

↓

Plot series B on graph

↓

Add labels and legend

↓

Show combined plot

↓

END

Load multiple time series data, plot them on the same graph with labels and legend, then display for comparison.

Execution Sample

Matplotlib

import matplotlib.pyplot as plt
import pandas as pd

# Create two time series data
series1 = pd.Series([1, 3, 2, 5, 7], index=pd.date_range('2024-01-01', periods=5))
series2 = pd.Series([2, 4, 1, 6, 8], index=pd.date_range('2024-01-01', periods=5))

plt.plot(series1.index, series1, label='Series 1')
plt.plot(series2.index, series2, label='Series 2')
plt.legend()
plt.show()

This code plots two time series on the same graph to compare their values over the same dates.

Execution Table

Step	Action	Data/Variables	Result/Output
1	Create series1	series1 = [1,3,2,5,7] with dates 2024-01-01 to 2024-01-05	series1 ready with 5 data points
2	Create series2	series2 = [2,4,1,6,8] with same dates	series2 ready with 5 data points
3	Plot series1	x=dates, y=series1 values	Line for series1 drawn on plot
4	Plot series2	x=dates, y=series2 values	Line for series2 drawn on plot
5	Add legend	labels: Series 1, Series 2	Legend displayed on plot
6	Show plot	Combined plot with both series	Graph window opens showing both lines
7	End	All plotting done	Execution stops

💡 All time series plotted and displayed, program ends

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 6
series1	None	[1,3,2,5,7] with dates	[1,3,2,5,7] with dates	[1,3,2,5,7] with dates
series2	None	None	[2,4,1,6,8] with dates	[2,4,1,6,8] with dates
plot	Empty	Empty	Empty	Displayed plot with both lines

Key Moments - 3 Insights

Why do both series use the same date range as the x-axis?

Both series are created with the same date index, so when plotting, the x-axis aligns perfectly for comparison, as shown in execution_table steps 1 and 2.

What happens if we plot series without labels?

Without labels, the legend would be empty or missing, making it hard to tell which line is which. Step 5 shows adding labels to fix this.

Why do we call plt.show() at the end?

plt.show() displays the plot window with all lines drawn. Without it, the plot may not appear. This is shown in step 6.

Visual Quiz - 3 Questions

Look at the execution_table at step 3. What is plotted on the x-axis?

A Dates from 2024-01-01 to 2024-01-05

B Values of series1

C Values of series2

D Legend labels

💡 Hint

Check the 'Data/Variables' column at step 3 in execution_table

At which step are both series visible on the plot?

A Step 3

B Step 5

C Step 4

D Step 6

💡 Hint

Look for when series2 is plotted in execution_table

If we remove plt.legend(), what changes in the output?

A No lines will be drawn

B Plot will show but no legend labels

C Plot will not show at all

D Series data will be lost

💡 Hint

Refer to step 5 in execution_table about adding legend

Concept Snapshot

Multiple time series comparison:
- Plot multiple series on same graph using plt.plot()
- Use same x-axis (time) for alignment
- Add labels and plt.legend() for clarity
- Call plt.show() to display
- Helps visually compare trends and values

Full Transcript

This visual execution shows how to compare multiple time series using matplotlib. First, two series with the same date range are created. Then each series is plotted on the same graph with their dates on the x-axis. Labels are added for clarity, and a legend is shown. Finally, plt.show() displays the combined plot. This method helps us see how two sets of data change over time side by side.

Practice

1. What is the main purpose of plotting multiple time series on the same graph using matplotlib?

easy

A. To make the graph load faster

B. To create separate graphs for each time series

C. To hide the data labels for clarity

D. To visually compare trends and differences between series over time

Solution

1. Step 1: Understand the purpose of multiple time series plots

   Plotting multiple lines on one graph helps us see how different series change over time side by side.

2. Step 2: Compare options with this purpose

   Only To visually compare trends and differences between series over time describes this visual comparison goal correctly.

3. Final Answer:

   To visually compare trends and differences between series over time -> Option D

4. Quick Check:

   Multiple time series comparison = Visual comparison [OK]

Hint: Multiple lines on one plot show trends side by side [OK]

Common Mistakes:

• Thinking multiple plots are created instead of one combined plot
• Ignoring the importance of labels and legends
• Believing it speeds up graph loading

2. Which of the following matplotlib code snippets correctly plots two time series series1 and series2 on the same graph with labels?

easy

A. plt.plot(series1, label='Series 1')
plt.legend()
plt.show()

B. plt.plot(series1)
plt.plot(series2)
plt.show()

C. plt.plot(series1, label='Series 1')
plt.plot(series2, label='Series 2')
plt.legend()
plt.show()

D. plt.plot(series1, label='Series 1')
plt.plot(series2, label='Series 2')
plt.show()

Solution

1. Step 1: Check for plotting both series with labels

   plt.plot(series1, label='Series 1') plt.plot(series2, label='Series 2') plt.legend() plt.show() plots both series and adds labels for each.

2. Step 2: Verify legend call to show labels

   plt.plot(series1, label='Series 1') plt.plot(series2, label='Series 2') plt.legend() plt.show() calls plt.legend() to display labels on the graph.

3. Final Answer:

   Code that plots both series with labels and shows legend -> Option C

4. Quick Check:

   Plot both + labels + legend = plt.plot(series1, label='Series 1') plt.plot(series2, label='Series 2') plt.legend() plt.show() [OK]

Hint: Always add labels and call plt.legend() to show them [OK]

Common Mistakes:

• Forgetting to call plt.legend() so labels don't appear
• Plotting only one series instead of both
• Not adding labels to each series

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

import matplotlib.pyplot as plt
series1 = [1, 3, 2, 4]
series2 = [2, 1, 3, 5]
plt.plot(series1, label='A')
plt.plot(series2, label='B')
plt.legend()
plt.show()

medium

A. A graph with two lines labeled 'A' and 'B' showing series1 and series2

B. A graph with one line showing the sum of series1 and series2

C. A graph with two lines but no labels

D. SyntaxError due to missing import

Solution

1. Step 1: Analyze the plotting commands

   Two lines are plotted: series1 with label 'A' and series2 with label 'B'.

2. Step 2: Check legend and show calls

   Calling plt.legend() displays the labels on the graph.

3. Final Answer:

   A graph with two lines labeled 'A' and 'B' showing series1 and series2 -> Option A

4. Quick Check:

   Two labeled lines plotted = A graph with two lines labeled 'A' and 'B' showing series1 and series2 [OK]

Hint: Labels appear only if plt.legend() is called [OK]

Common Mistakes:

• Thinking lines are summed instead of plotted separately
• Forgetting plt.legend() hides labels
• Assuming syntax error without import

4. The following code is intended to plot two time series with labels, but the legend does not appear. What is the error?

import matplotlib.pyplot as plt
series1 = [1, 2, 3]
series2 = [3, 2, 1]
plt.plot(series1, label='First')
plt.plot(series2, label='Second')
plt.show()

medium

A. Missing plt.legend() call to display the legend

B. Labels are incorrectly assigned inside plt.plot()

C. plt.show() should be called before plotting

D. series2 should be plotted before series1

Solution

1. Step 1: Check for legend display code

   The code does not call plt.legend(), so labels won't show.

2. Step 2: Confirm label usage is correct

   Labels are correctly passed in plt.plot(), so no issue there.

3. Final Answer:

   Missing plt.legend() call to display the legend -> Option A

4. Quick Check:

   Legend missing without plt.legend() [OK]

Hint: Always add plt.legend() to show labels on plot [OK]

Common Mistakes:

• Assuming labels show automatically without legend call
• Thinking order of plotting affects legend display
• Calling plt.show() too early

5. You have three time series with different lengths:
series1 = [1, 2, 3, 4], series2 = [2, 3, 4], series3 = [1, 3, 5, 7, 9].
How can you correctly plot all three on the same graph to compare them over time?

hard

A. Plot all series using the length of the longest series only

B. Plot each series with its own x-axis range matching its length, then add labels and legend

C. Pad shorter series with zeros to match the longest series length before plotting

D. Plot only the shortest series to avoid errors

Solution

1. Step 1: Understand different lengths require matching x-axis

   Each series must be plotted with x values matching its length to avoid misalignment.

2. Step 2: Plot each series with its own x range and add labels

   Use range(len(series)) for x-axis, plot all, then add labels and legend.

3. Final Answer:

   Plot each series with its own x-axis range matching its length, then add labels and legend -> Option B

4. Quick Check:

   Match x-axis length per series + labels = Plot each series with its own x-axis range matching its length, then add labels and legend [OK]

Hint: Use range(len(series)) for x-axis of each series [OK]

Common Mistakes:

• Plotting all series without adjusting x-axis causes misaligned lines
• Padding with zeros changes data meaning
• Ignoring series length differences