Multidimensional Arrays

1
Multidimensional Arrays
2
Goals

• By the end of this lecture you should
• Understand how to program parallel arrays.
• Understand how to create two-dimensional arrays.
• Understand how to access elements in a
  two-dimensional array.

3
Parallel (Corresponding) Arrays

• Parallel arrays give you the ability to store
  multiple pieces of information about a single
  entity in an application.
  
• The subscripts of each array should correspond to
  one another for individual entities.

4
Conceptual Example of Parallel Arrays
fltExam1Scores
strStudents
strSID
5
Creating Parallel Arrays

• To create parallel arrays, just create them as
  you would any other arrayvar strSID new
  Array()var strStudents new Array() var
  fltExamScores new Array()
• The arrays are separate arrays in memory, treat
  them as one in your application

6
Assigning Values to Parallel Arrays

• To assign values for a single entity to parallel
  arrays, use the same index number for each
  assignmentstrSID5 025769strStudents5
  RavifltExamScores5 .82

7
Take the next few minutes to examine the file
called multidimensionalArrays_01.html.
8
Another Approach

• Another way that we can model tables of data is
  to use a multidimensional array.
  
• A multidimensional array is an "array of arrays."
  When we use one, we need to specify multiple
  index numbers to assign/read elements.

9
Creating a 2-D Array

• To create a 2-D array, we first declare a simple
  arrayvar arr2D_Array new Array()
  
• Then, for each "row" that we add to the 2D array,
  we create a new array in an index of the parent
  arrayarr2D_Array0 new Array()

10
Accessing 2D Array Elements

• To read or assign values to elements in a 2D
  array, we need to specify two subscripts. The
  first is the "row" number (from the parent) the
  second represents the "column" number (from the
  child) arr2D_Array00 "Hi"

11
Schematic Model of a 2D Array
Child (Second) Subscript
Parent (First) Subscript
12
Take the next few minutes to examine the file
called multidimensionalArrays_02.html.
13
Summary

• We can use parallel arrays to store information
  about a single entity across multiple arrays.
  
• In a set of parallel arrays, we store values
  related to a single entity so they share the same
  subscript number across the arrays in the
  parallel set.
• continued

14
Summary

• Multidimensional arrays are arrays of arrays.
• We can use a two-dimensional array to model a
  table of data. The rows represent the subscripts
  from the parent array the columns represent the
  subscripts from the children arrays.
• continued

15
Summary

• In a two-dimensional array, we access array
  elements by specifying two subscripts the first
  representing the "row" number (from the parent)
  and the second representing the "column" number
  (from the child).