6: Arrays and Collections

Transcription

1 6: Arrays and Collections Andrew Cumming, SoC Bill Buchanan, SoC W.Buchanan (1)

2 Course Outline Day 1: Morning Introduction to Object-Orientation, Introduction to.net, Overview of.net Framework,.NET Components. C#. Introduction to Visual Studio Environment. Day 1: Afternoon Variables and Types, Naming Variables, Using Built-In Data Types, Visual Studio Environment: Design Surface - dynamic help; Toolbox; Code Page; Properties Window; Solution Explorer. Day 2: Morning Converting Data Types, Control structures: if, for, while, foreach, switch. Day 2: Afternoon File handling looking up details from help, Methods, Parameter passing, Variables and scope. Day 3: Morning REVIEW OF BASICS FROM DAY 2, Converting Data Types, Control structures: if, for, while, foreach, switch. Day 3: Afternoon Brief description of Arrays, Type Casts, Overview of System.Collections, ArrayLists and HashTables, Sorting, Enumerators Course Outline (Day 1 to 3) W.Buchanan (2)

3 Course Outline Day 4: Morning Using Reference-Type Variables, Using Common Reference Types, The Object Hierarchy, Namespaces in the.net Framework, Debugging techniques, breakpoints, line stepping, call stack, locals window. Day 4: Afternoon - Classes and Objects, Using Encapsulation, C# and Object Orientation, Defining Object-Oriented Systems, Deriving classes, Implementing classes, Private, public, internal and protected, Using Interfaces, Abstract classes, Using Constructors Initializing Data, Objects and Memory, Resource Management, Object Browser, Class View. Day 5: Morning - Methods and overloaded methods, Exceptions, Intellisense and overloaded methods, Enumerations and string enumeration conversion. Day 5: Afternoon: Using Modules and Assemblies, XML (read only), Serialising classes. Course Outline (Day 4 and 5) W.Buchanan (3)

4 Module 6 Arrays. Reading from CSV files. System.Collections. ArrayLists. HashTables. Introduction W.Buchanan (4)

5 Arrays W.Buchanan (5)

6 System.Array object: Methods include: BinarySearch() Clear() Clone() Copy() CopyTo() CreateInstance() GetLength() IndexOf() Initialize() LastIndexOf() Reverse() SetValue() Sort() IsFixedSize IsReadOnly Length Performs a binary on a one-dimensional array Sets a range of elements to zero, False or NULL. Make a shallow copy of the array. Copies a range of values in an array. Copies one array to another. Create a multidimensional array. Return the number of elements in the array. Search for an object, and return the first index value of its place. Set all the elements in the array to their default value. Returns the last object in the array. Reverses the array. Sets a specific array element to a value. Performs a sort on the array. Identifies if the array is a fixed size (get only) Identifies if the array is read-only (get only) Identifies the length of the array (get only) W.Buchanan (6)

7 Variables ArrayName i j Reference to the start of the array space. Element 0 Element 1 Element 2 k Allocated on the heap. Element 3 Element 4 Element n-2 Element n-1 Variables and Arrays W.Buchanan (7)

8 W.Buchanan (8)

9 C# contains the methods of the System.Array object. It also inherits the syntax of C for representing an array index, which uses square brackets to identify the element, such as: myarray[15]; for the element number 15. Note that C# starts its indexing at 0, thus myarray[15] is the 16th element of the array. To declare an array: type[] arrayname; For example to declare an array of doubles: double[] inputvalues; This declares the type of the array. To then to initialize it the following is used: inputvalues = new double[5]; which creates a new array with 5 elements (0 to 4). ArrayName Element 0 Element 1 Element 2 Element 3 Element 4 Element n-2 Element n-1 W.Buchanan (9)

10 namespace ConsoleApplication2 class ArrayExample01 static void getvalues(double[] v) int i; for (i=0;i<v.length;i++) System.Console.Write("Value >> "); v[i]=convert.todouble(system.console.readline()); static double average(double[] v) double total=0; int i; for (i=0;i<v.length;i++) total+=v[i]; return(total/v.length); static void Main(string[] args) int i; double[] inputvalues; double av; inputvalues = new double[5]; getvalues(inputvalues); av=average(inputvalues); System.Console.WriteLine("Average is 0",av); System.Console.ReadLine(); W.Buchanan (10)

11 Note that the declaration of the array type does not actually create the array, and the line: double[] inputvalues; double av av=inputvalues[0]; will cause a build error of: Use of unassigned local variable 'inputvalues' As the array can not been created yet, and just contains a null value. Using an array W.Buchanan (11)

12 The arrays when they are initialized are set to a default value, such as zero for numeric data types, and null for strings. To initialise it with actual values, the required values are contained within curly brackets, such as: double[] vals = 1.2,1.4,1.6,1.8,2.0; string[] menuitems = "File", "Edit", "View", "Insert", "Tool", "Table"; This performs both the declaration of the array and its initialization. Program 3.2 shows an example of the declaration of an array of strings. W.Buchanan (12)

13 using System; namespace ConsoleApplication2 class ArrayExample01 static void Main(string[] args) int i; string[] ColourBands="BLACK","BROWN","RED","ORANGE","YELLOW", "GREEN"; for (i=0;i<colourbands.length;i++) System.Console.WriteLine("0 is 1",i,ColourBands[i]); System.Console.ReadLine(); W.Buchanan (13)

14 using System; namespace ConsoleApplication2 class ArrayExample01 static double findsmallest(double[] v) double smallest; smallest=v[0]; for (int i=1; i<v.length; i++) if (v[i]<smallest) smallest = v[i]; return(smallest); static void Main(string[] args) int i; double[] vals = 1.2,4.5,13.3,10.1,-4.3,52.5,6.2; double smallest; smallest= findsmallest(vals); System.Console.WriteLine("Smallest value is 0",smallest); System.Console.ReadLine(); W.Buchanan (14)

15 foreach W.Buchanan (15)

16 foreach (type identifier in expression) statement Thus: for (i=0;i<colourbands.length;i++) System.Console.WriteLine("0 is 1",i,ColourBands[i]); is replaced by (Program3_3_ArrayInitializationNumericForEach): foreach (string band in ColourBands) System.Console.WriteLine("0",band); For the example in Program 3.2 we can replace: for (int i=1; i<v.length; i++) if (v[i]<smallest) smallest = v[i]; with (Program3_4_ArrayInitializationStringsForEach): foreach (double val in v) if (val<smallest) smallest = val; foreach W.Buchanan (16)

17 using System; namespace ConsoleApplication2 class ArrayExample01 static double findsmallest(double[] v) double smallest; smallest=v[0]; foreach (double val in v) if (val<smallest) smallest = val; return(smallest); static void Main(string[] args) int i; double[] vals = 1.2,4.5,13.3,10.1,-4.3,52.5,6.2; double smallest; smallest= findsmallest(vals); System.Console.WriteLine("Smallest value is 0",smallest); System.Console.ReadLine(); W.Buchanan (17)

18 Tutorial Session 6.1: Q6.1 to Q6.4 Presentations Notes SourceCode Tutorials W.Buchanan (18)

19 namespace solution6_04 class Class1 static void finderror(double[] a1, double[] a2, double[] a3) for (int i=0; i<a1.length; i++) a3[i]=a1[i]-a2[i]; static void Main(string[] args) double[] array01 = 3, 3.1, 4.3, 5.5, 6.7, 5.4, 3.1, 4.4; double[] array02 = 3.1, 3.3, 4.1, 6.5, 6.65, 5.21, 3.11, 4. double[] array03 = 0,0,0,0,0,0,0,0; finderror(array01, array02, array03); for (int i=0;i<array03.length;i++) System.Console.WriteLine("0\t1\t2", array01[i],array02[i],array03[i]); System.Console.ReadLine(); W.Buchanan (19)

20 Reading CSV Data W.Buchanan (20)

21 1,5,6,7,4,5,6,7,10,5,4,3,2,1 For this we can read the file one line at a time, and then split the string using the Split() method. This can be contained with the foreach statement, to parse each part of the split text. The code which fills the array v is: do text=reader.readline(); if (text==null) break; foreach (string substring in text.split(',')) v[i]=convert.todouble(substring); i++; while (text!= null); Reading a CSV file W.Buchanan (21)

22 class ArrayExample02 const int ARRAYLIMIT=100; static void filldata(double[] v) int i=0; FileInfo thesourcefile = new FileInfo("..\\..\\test.csv"); StreamReader reader = thesourcefile.opentext(); string text; do text=reader.readline(); if (text==null) break; foreach (string substring in text.split(',')) v[i]=convert.todouble(substring); i++; while (text!= null); reader.close(); W.Buchanan (22)

23 Often the CSV file is organised into rows with comma separated variables in each row. This is similar to a spreadsheet where the row is represented by a line, and the columns are delimited by commas. For example: Fred,20 Bert,10 Colin,15 Berty,26 Freddy,22 We can then modify the reading method to parse the input line from the CSV file: do text=reader.readline(); if (text==null) break; string[] str =text.split(','); name[i]=str[0]; age[i]=convert.toint32(str[1]); i++; while (text!= null); CSV W.Buchanan (23)

24 Tutorial Session 5.2: Q6.5 to Q6.7 Presentations Notes SourceCode Tutorials W.Buchanan (24)

25 Collections W.Buchanan (25)

26 System.Collections ArrayList BitArray CaseInsensitiveComparer CaseInsensitiveHashCodeProvider CollectionBase Comparer DictionaryBase DictionaryEntry Hashtable Queue ReadOnlyCollectionBase SortedList Stack W.Buchanan (26)

27 ArrayLists W.Buchanan (27)

28 System.Array object: Methods include: BinarySearch() Clear() Clone() Copy() CopyTo() CreateInstance() GetLength() IndexOf() Initialize() LastIndexOf() Reverse() SetValue() Sort() IsFixedSize IsReadOnly Length Performs a binary on a one-dimensional array Sets a range of elements to zero, False or NULL. Make a shallow copy of the array. Copies a range of values in an array. Copies one array to another. Create a multidimensional array. Return the number of elements in the array. Search for an object, and return the first index value of its place. Set all the elements in the array to their default value. Returns the last object in the array. Reverses the array. Sets a specific array element to a value. Performs a sort on the array. Identifies if the array is a fixed size (get only) Identifies if the array is read-only (get only) Identifies the length of the array (get only) W.Buchanan (28)

29 using System; using System.Collections; namespace ConsoleApplication2 class Class1 static void Main(string[] args) ArrayList a = new ArrayList(); a.add("arnold"); a.add("smith"); a.add("cordiner"); a.add("mitchel"); a.sort(); foreach (string nam in a) System.Console.WriteLine("0",nam); System.Console.ReadLine(); W.Buchanan (29)

30 namespace ConsoleApplication2 using System; using System.Collections; // required for ArrayList using System.IO; // required for File I/O class ArrayExample02 static void filldata(arraylist v) int i=0; FileInfo thesourcefile = new FileInfo("..\\..\\test.csv"); StreamReader reader = thesourcefile.opentext(); string text; do text=reader.readline(); if (text==null) break; foreach (string substring in text.split(',')) v.add(convert.todouble(substring)); i++; while (text!= null); reader.close(); W.Buchanan (30)

31 static void showdata(arraylist v) int i; for (i=0;i<v.count;i++) Console.WriteLine("0 1",i,v[i]); static void Main(string[] args) ArrayList Vals = new ArrayList(); filldata(vals); showdata(vals); System.Console.ReadLine(); W.Buchanan (31)

32 static void showdata(arraylist v) 0 1 int i; 1 5 for (i=0;i<v.count;i++) 2 6 Console.WriteLine("0 1",i,v[i]); static void Main(string[] args) ArrayList Vals = new ArrayList(); filldata(vals); showdata(vals); System.Console.ReadLine(); W.Buchanan (32)

33 namespace ConsoleApplication2 using System; using System.Collections; // required for ArrayList using System.IO; // required for File I/O class ArrayExample02 static void filldata(arraylist v) int i=0; FileInfo thesourcefile = new FileInfo("..\\..\\test.csv"); StreamReader reader = thesourcefile.opentext(); string text; do text=reader.readline(); if (text==null) break; foreach (string substring in text.split(',')) v.add(convert.todouble(substring)); i++; while (text!= null); reader.close(); W.Buchanan (33)

34 static void showdata(arraylist v) for (int i=0;i<v.count;i++) Console.WriteLine("0 1",i,v[i]); static double findaverage(arraylist v) double total=0; for (int i=0;i<v.count;i++) total+=convert.todouble(v[i]); return(total/v.count); static void Main(string[] args) ArrayList Vals = new ArrayList(); double average; filldata(vals); average=findaverage(vals); System.Console.WriteLine("Average is 0",average); System.Console.ReadLine(); W.Buchanan (34)

35 namespace ConsoleApplication2 using System; using System.Collections; // required for ArrayList using System.IO; // required for File I/O class ArrayExample02 static void filldata(arraylist v) int i=0; FileInfo thesourcefile = new FileInfo("..\\..\\test.csv"); StreamReader reader = thesourcefile.opentext(); string text; do text=reader.readline(); if (text==null) break; v.add(text); while (text!= null); reader.close(); W.Buchanan (35)

36 static void showdata(arraylist v) int i; for (i=0;i<v.count;i++) Console.WriteLine("0 1",i,v[i]); static void Main(string[] args) ArrayList Vals = new ArrayList(); filldata(vals); showdata(vals); Vals.Sort(); showdata(vals); System.Console.ReadLine(); W.Buchanan (36)

37 static void showdata(arraylist v) int i; for (i=0;i<v.count;i++) Console.WriteLine("0 1",i,v[i]); static void Main(string[] args) ArrayList Vals = new ArrayList(); filldata(vals); showdata(vals); Vals.Sort(); showdata(vals); System.Console.ReadLine(); 0 Smith,Fred 1 Bell,Bert 2 McDonald,Rory 3 Mitchel,Brian 4 Barr,Martin 5 Kinlock,Graha 0 Barr,Martin 1 Bell,Bert 2 Kinlock,Graha 3 McDonald,Rory 4 Mitchel,Brian 5 Smith,Fred W.Buchanan (37)

38 Tutorial Session 5.2: Q6.8 to Q6.9 Presentations Notes SourceCode Tutorials W.Buchanan (38)

39 HashTables # W.Buchanan (39)

40 HashTables represents a collection of key-and-value pairs that are organized based on the hash code of the key. They are particularly useful for fast retrieval of data from a list. They are basically dictionaries of data. Array HashTable 0 Fred Smith AB01 Fred Smith Bert Smith Fred Jones Sally Smith Andy Forbes CD01 DE02 AB02 DE02 Bert Smith Fred Jones Sally Smith Andy Forbes W.Buchanan (40)

41 Add(object,object) Adds elements with a specified key and value into the Hashtable. Clear() Removes the elements in Hashtable. Clone() Creates a shallow copy of the Hashtable. Contains(object) Determines whether the Hashtable contains a certain key. ContainsValue(object) Determines whether the Hashtable contains a certain value. CopyTo(System.Array,int) Copies a parts of a Hashtable to a one-dimensional Array instance. GetEnumerator() Returns an enumerator value that can iterate through the Hashtable. W.Buchanan (41)

42 GetHash(object) Returns the hash code for the specified key. Hashtable(int) Create a empty Hashtable. Hashtable() Creates an empty Hashtable. KeyEquals(object,object) Compares an object with the key. Remove(object) Removes the element with the specified key from the Hashtable. W.Buchanan (42)

43 using System; using System.Collections; namespace ConsoleApplication1 class Class1 static void Main(string[] args) Hashtable h = new Hashtable(); Name:Fred Smith Name:Bert Smith Name:Fred Jones h.add("a000","fred Smith"); h.add("b111","bert Smith"); h.add("c232","fred Jones"); System.Console.WriteLine("Name:0",h["A000"]); System.Console.WriteLine("Name:0",h["B111"]); System.Console.WriteLine("Name:0",h["C232"]); System.Console.ReadLine(); W.Buchanan (43)

44 using System; using System.Collections; namespace ConsoleApplication1 class Class1 static void Main(string[] args) Hashtable h = new Hashtable(); Name: Name: Name: h.add("a000","fred Smith"); h.add("b111","bert Smith"); h.add("c232","fred Jones"); h.clear(); System.Console.WriteLine("Name:0",h["A000"]); System.Console.WriteLine("Name:0",h["B111"]); System.Console.WriteLine("Name:0",h["C232"]); System.Console.ReadLine(); W.Buchanan (44)

45 The Hashtable uses a similar technique to add data to its list (with the Add() method). Once the table has been filled, the keys from the table can be generated from (using a Hashtable of v): ICollection keys = v.keys; And the values in the list by: ICollection values = v.values; W.Buchanan (45)

46 using System; using System.Collections; namespace ConsoleApplication1 class Class1 static void Main(string[] args) Hashtable h = new Hashtable(); h.add("a000","fred Smith"); h.add("b111","bert Smith"); h.add("c232","fred Jones"); ICollection keys = h.keys; ICollection values = h.values; System.Console.WriteLine("Keys are: "); foreach (string key in keys) Console.WriteLine("0",key); System.Console.WriteLine("Values are: "); foreach (string val in values) Console.WriteLine("0",val); System.Console.ReadLine(); W.Buchanan (46)

47 using System; using System.Collections; namespace ConsoleApplication1 class Class1 static void Main(string[] args) Hashtable h = new Hashtable(); h.add("a000","fred Smith"); h.add("b111","bert Smith"); h.add("c232","fred Jones"); ICollection keys = h.keys; ICollection values = h.values; System.Console.WriteLine("Keys are: "); foreach (string key in keys) Console.WriteLine("0",key); System.Console.WriteLine("Values are: "); foreach (string val in values) Console.WriteLine("0",val); System.Console.ReadLine(); Keys are: C232 A000 B111 Values are: Fred Jones Fred Smith Bert Smith W.Buchanan (47)

48 static void showdata(hashtable v) int i; ICollection keys = v.keys; ICollection values = v.values; System.Console.WriteLine("Keys are: "); foreach (string key in keys) Console.WriteLine("0",key); System.Console.WriteLine("Values are: "); foreach (string val in values) Console.WriteLine("0",val); W.Buchanan (48)

49 It is possible to browse through the dictionary by creating an enumerator (using the GetEnumerator() method). This creates a list of references to the elements in the hashtable. This is achieved with the following (for a hashtable of v): System.Collections.IDictionaryEnumerator enumerator = v.getenumerator(); while (enumerator.movenext()) Console.WriteLine("0 1",enumerator.Key, enumerator.value); W.Buchanan (49)

50 using System; using System.Collections; namespace ConsoleApplication1 class Class1 static void Main(string[] args) Hashtable h = new Hashtable(); h.add("a000","fred Smith"); h.add("b111","bert Smith"); h.add("c232","fred Jones"); System.Collections.IDictionaryEnumerator enumerator = h.getenumerator(); while (enumerator.movenext()) Console.WriteLine("0 1",enumerator.Key, enumerator.value); System.Console.ReadLine(); W.Buchanan (50)

51 using System; using System.Collections; namespace ConsoleApplication1 class Class1 static void Main(string[] args) Hashtable h = new Hashtable(); C232 Fred Jones A000 Fred Smith B111 Bert Smith h.add("a000","fred Smith"); h.add("b111","bert Smith"); h.add("c232","fred Jones"); System.Collections.IDictionaryEnumerator enumerator = h.getenumerator(); while (enumerator.movenext()) Console.WriteLine("0 1",enumerator.Key, enumerator.value); System.Console.ReadLine(); W.Buchanan (51)

52 Tutorial Session 5.2: Q6.10 to Q6.12 Presentations Notes SourceCode Tutorials W.Buchanan (52)