Arrays: PHP 7 Complete Guide: Simple, Multi-dimensional, Associative, and Object Arrays (2016)
Chapter 2. Multi-dimensional Arrays
Chapter 3. Associative and Object Arrays
Chapter 4. PHP Functions - Changing, Spliting, Slicing, and Sorting Arrays
Chapter 5. PHP Functions - Comparing and Merging Arrays
Chapter 6. PHP Functions - Searching, Traversing, and Displaying Arrays