Unit 4 – Data Collections: Overview

• Date: 12/18/2025
• Sections:
  • 4.1 Ethical and Social Issues Around Data Collection
  • 4.2 Introduction to Using Data Sets
  • 4.3 Array Creation and Access
  • 4.4 Array Traversals
  • 4.5 Implementing Array Algorithms

4.1 Ethical and Social Issues Around Data Collection

• Impact of Computing on Society, Economy, and Culture:
  • Society:
  • Communication and social interaction enhancement.
  • Improvements in education and healthcare.
  • Economy:
  • Job creation through automation and globalization.
  • However, risks of job displacement and gig economy instability.
  • Culture:
  • Loss of traditions and preservation of culture through digital means.
  • Risks associated with online misinformation.
• Privacy Risks:
  • Concerns regarding personal information exposure when using computers.
  • Importance of limiting data collection to necessary information.
  • Questions regarding data storage and access rights to personal data.

4.2 Introduction to Using Data Sets

• Definition of Data Set:
  • A collection of specific pieces of information or data, manipulable and analyzable to solve a problem or answer a question.
• Sources of Data Sets:
  • Free online resources, including:
  • US Department of Education College Scorecard
  • data.gov
  • kaggle.com
  • Google Dataset Search
  • Considerations for data usage: the necessity for trimming, cleaning data, and addressing privacy issues.

4.3 Array Creation and Access

4.3.1 Declaring and Creating an Array

• Definition of Array:
  • A fixed-length indexed list of values of the same type, can be an object or primitive type.
  • Example Declaration:
  • double[] numbers = new double[10];

4.3.2 Using new to Create Arrays

• Creates a new instance of an array.
• Example of fixed-length creation:
  • double[] numbers = new double[10]; creates a storage for 10 doubles.

4.3.3 Initializer Lists to Create Arrays

• Arrays can be initialized directly with specified values:
  • int[] perfectSquares = {1, 4, 9, 16};
• This notation allows for immediate assignment of initial values to an array.

4.3.4 Array Length

• Accessed with the property length (no parentheses).
• Example of using length in loops:
  • for (int i = 0; i < tens.length; i++) { ... }

4.3.5 Access and Modify Array Values

• Accessing a specific index can be done as follows:
  • states[0] = "Florida";
  • Output via System.out.println(states[1]);
• Attempting to access out-of-bounds index results in an error (ArrayIndexOutOfBoundsException).

4.3.6 Coding Challenge: Countries Array

• Students can practice creating arrays with real-world applications, such as storing country names.

4.3.7 Design an Array of Objects for your Community

• Encourage participation by creating arrays that reflect community structure or demographics.

4.3.8 Summary

• Recap on array declaration, creation, initialization, and accessing/modifying values.

4.3.9 AP Practice

• Practical application exercises to reinforce learning objectives.

4.4 Array Traversals

4.4.1 Index Variables

• Index values start at 0 and increment according to the array length.

4.4.2 Loops to Traverse Arrays

• Example Java code demonstrating traversal:
  • for (int i = 0; i < tens.length; i++) { tens[i] = (i+1)*10; }
• Importance of utilizing intact conditions to avoid errors during array traversals.

4.4.3 Arrays as Objects and Parameters

• Arrays can be passed to methods, encouraging modular programming.

4.4.4 Looping through Part of an Array

• Partial array traversal methods to focus calculations or searches on specific array segments.

4.4.5 Common Errors When Looping Through an Array

• Frequently arose confusion about zero-indexing and handling array boundaries.

4.4.6 Enhanced For-Loop (For-Each) for Arrays

• Simplified iteration over array elements:
  • for (double e : data) { sum += e; }

4.4.7 Enhanced For Loop Limitations

• Not suitable for scenarios requiring index manipulation (e.g., updating specific array elements).

4.4.8 Traversing Arrays of Objects

• Encourages insight into accessing properties of object arrays.

4.4.9 Coding Challenge: SpellChecker

• Implementing dictionary checks using an array of strings for spell checking.

4.4.10 Design an Array of Objects for your Community

• Prompting students to develop arrays integral to community representation.

4.4.11 Summary

• Reinforcing concepts from array traversals and their applications.

4.4.12 Arrays Game Turn into eCampus!

• Section dedicated to practical applications engaging with e-learning platforms.

4.5 Implementing Array Algorithms

4.5.1 Accumulator Pattern for Sum/Average

• Utilizing loops to compute statistical properties of arrays.

4.5.2 Min, Max, Search Algorithms

• Algorithms described for finding minimum and maximum values, along with executing search operations within arrays.

4.5.3 Looping from Back to Front

• Techniques illustrating reverse iteration through arrays.

4.5.4 Test Property

• Implementing tests to check array properties or conditions.

4.5.5 Pairs and Duplicates in Arrays

• Algorithms recognizing and counting pairs or duplicate elements.

4.5.6 Rotating Array Elements

• Routines to manage rotation of array contents.

4.5.7 Reversing an Array

• Example algorithm for reversing contents:
  • Code that swaps indices till the mid-point is reached.

4.5.8 Review and FRQ Practice for Arrays

• Section aimed at consolidating knowledge through further challenges.

Final Projects and Coding Challenges

Project 4.1 – Array Algorithms with Grades

• A GradesList class designed to compute averages, count grades above a score, and determine maximum grades alongside failure check:
  • Method Definitions:
  • average(): Returns overall average.
  • gradesAbove(double value): Counts grades above the given parameter.
  • maxGrade(): Identifies the highest grade from the list.
  • noFailures(): Evaluates presence of scores below 60.

Examples of Grades Calculation Outputs

• Example outputs to match against project submissions emphasizing correct implementation.

Advanced Array Algorithms

Typical Algorithms

• Addressing the detection of increasing sequences and the presence of duplicates within arrays:
  • Increasing Sequence Algorithm: Uses a loop to affirm that consecutive elements increase.
  • Duplicate Detection: Scans pairs through nested loops identifying if any two elements are the same.

Shifting and Reversing

• Techniques defined for shifting elements left or right and for reversing element order within an array.

Review for Test 4A

• Resources provided:
  • CSAwesome: Optional coding practices.
  • AP Classroom Exercises: Including MCQ part and FRQ assignments to test student knowledge.