Video: Multidimensional Arrays in C# (Bulgarian)

Topics covered:

• Matrices and Multidimensional Arrays
  • Declaring
  • Usage
• Jagged Arrays
  • Declaring
  • Usage
• The Array Class
  • Sorting
  • Binary Search

Video (in Bulgarian)

Presentation Content

What is Multidimensional Array?

• Multidimensional arrays have more than one dimension (2, 3, …)
  • The most important multidimensional arrays are the 2-dimensional
    • Known as matrices or tables
• Example of matrix of integers with 2 rows and 4 columns:

Declaring and Creating Multidimensional Arrays

• Declaring multidimensional arrays:
• Creating a multidimensional array
  • Use new keyword
  • Must specify the size of each dimension

Initializing Multidimensional Arrays with Values

• Creating and initializing with values multidimensional array:
  • Matrices are represented by a list of rows
    • Rows consist of list of values
  • The first dimension comes first, the second comes next (inside the first)

Jagged Arrays

• Jagged arrays are like multidimensional arrays
  • But each dimension has different size
  • A jagged array is array of arrays
  • Each of the arrays hasdifferent length
• How to create jagged array?

Initialization of Jagged Arrays

• When creating jagged arrays
  • Initially the array is created of null arrays
  • Need to initialize each of them

Example of Jagged Arrays

• Check a set of numbers and group them by their remainder when dividing to 3 (0, 1 and 2)
• Example: 0, 1, 4, 113, 55, 3, 1, 2, 66, 557, 124, 2
• First we need to count the numbers
  • Done with a iteration
• Make jagged array withappropriate sizes
• Each number is addedinto its jagged array

The Array Class

• The System.Array class
  • Parent of all arrays
  • All arrays inherit from it
  • All arrays have the same:
    • Basic functionality
    • Basic properties
    • E.g. Length property

Methods of Array

• Important methods and properties of System.Array
  • Rank – number of dimensions
  • Length – number of all elements through all dimensions
  • GetLength(index) – returns the number of elements in the specified dimension
    • Dimensions are numbered from 0

Methods of Array (2)

• GetEnumerator() – returns IEnumerator for the array elements
• BinarySearch (…) – searches for a given element into a sorted array (uses binary search)
• IndexOf (…) – searches for a given element and returns the index of the first occurrence (if any)
• LastIndexOf(…) – searches for a given element and returns the last occurrence index
• Copy(src, dest, len) – copies array elements; has many overloads
• Reverse (…) – inverts the arrays elements upside down
• Clear (…) _ _ – assigns value 0 (null) for each elements
• CreateInstance (…) _ _ – creates an array
  • Accepts as parameters the number of dimensions, start index and number of elements
• Implements ICloneable , IList , ICollection and IEnumerable interfaces

Sorting Arrays

• Sorting in .NET is usually done with System.Array.Sort()
  • Sort(Array) – sorts array elements
    • Elements should implement IComparable
  • Sort(Array, _ _ IComparer) – sorts array elements by given external IComparer
  • Sort(Array, _ _ Comparison<T>) – sorts array elements by given comparison operation
    • Can be used with lambda expression

Binary Search

• Binary search is a fast method for searching for an element in a sorted array
  • Has guaranteed running time of O(log(n)) _ _ for searching among arrays of with n elements
• Implemented in the Array.BinarySearch( Array, object) method
  • Returns the index of the found object or a negative number when not found
• All requirements of the Sort() method are applicable for BinarySearch()
  • Either all elements should implement IComparable<T> or instance of IComparer<T> should be passed

Advices for Working with Arrays

• When given method returns an array and should return an empty array (array with 0 elements) instead of null
• Arrays are passed by reference
  • To be sure that given method will not change the passed array, pass a copy of it
• Clone() returns shallow copy of the array
  • You should implement your own deep clone when working with reference types