Lecture Notes: Constructing a Bar Graph with R

Overview

• Purpose: To learn how to construct a bar graph showing proportions using R programming.
• Example Context: Population in Park City categorized into children, working-age adults, and retirees.

Understanding the Data

• Frequency Table:
  • Displays number of people in each category (frequency).
  • Shows percentage each category makes up (relative frequency).

Constructing the Bar Graph

Key Components Needed

1. Categories

   • Used to label each bar.
   • Example: Age groups (children, working-age adults, retirees).

2. Heights

   • Heights correspond to the proportions of each category.
   • Example: Proportion percentages from the table.

Using R for Bar Graph

• Use barplot() function to construct the graph.

Steps to Create Bar Graph in R

1. Define Heights: Proportions List

   • Use c() to combine values into a list.
   • Values from the last column of the table (proportions):
     • 19.11%, 43.37%, 37.52%
   • Assign to a variable: proportions

2. Define Labels: Age Groups List

   • Use c() to create list of age groups.
   • Ensure values are in double quotes: "children", "working age adults", "retirees".
   • Assign to a variable: ageGroups

3. Construct Bar Plot

   • Call barplot() function:
     • Heights parameter: proportions
     • Labels parameter: ageGroups
   • Ensure correct order alignment between the heights and names lists.

Considerations

• Use double quotes for text labels to avoid computation errors.
• Maintain consistent order in lists for accurate plotting.

Outcome

• R creates a bar chart based on provided data:
  • Bars labeled: Children, Working-age adults, Retirees.
  • Heights: Close to expected proportions (19.11%, 43.37%, 37.52%).

Conclusion

• By giving the computer the necessary data, it can automate the construction of a bar chart.
• Understanding how to prepare data and use R functions are key steps in visual data representation.