How can I search an array in VB.NET?

Question

I want to be able to effectively search an array for the contents of a string.
Example:

dim arr() as string={"ravi","Kumar","Ravi","Ramesh"}

I pass the value is "ra" and I want it to return the index of 2 and 3.

How can I do this in VB.NET?

Answer 1

Dim inputString As String = "ra"
Enumerable.Range(0, arr.Length).Where(Function(x) arr(x).ToLower().Contains(inputString.ToLower()))

Answer 2

This would do the trick, returning the values at indeces 0, 2 and 3.

Array.FindAll(arr, Function(s) s.ToLower().StartsWith("ra"))

Answer 3

If you want an efficient search that is often repeated, first sort the array (Array.Sort) and then use Array.BinarySearch.

Answer 4

It's not exactly clear how you want to search the array. Here are some alternatives:

Find all items containing the exact string "Ra" (returns items 2 and 3):

Dim result As String() = Array.FindAll(arr, Function(s) s.Contains("Ra"))

Find all items starting with the exact string "Ra" (returns items 2 and 3):

Dim result As String() = Array.FindAll(arr, Function(s) s.StartsWith("Ra"))

Find all items containing any case version of "ra" (returns items 0, 2 and 3):

Dim result As String() = Array.FindAll(arr, Function(s) s.ToLower().Contains("ra"))

Find all items starting with any case version of "ra" (retuns items 0, 2 and 3):

Dim result As String() = Array.FindAll(arr, Function(s) s.ToLower().StartsWith("ra"))

-

If you are not using VB 9+ then you don't have anonymous functions, so you have to create a named function.

Example:

Function ContainsRa(s As String) As Boolean
   Return s.Contains("Ra")
End Function

Usage:

Dim result As String() = Array.FindAll(arr, ContainsRa)

Having a function that only can compare to a specific string isn't always very useful, so to be able to specify a string to compare to you would have to put it in a class to have somewhere to store the string:

Public Class ArrayComparer

   Private _compareTo As String

   Public Sub New(compareTo As String)
      _compareTo = compareTo
   End Sub

   Function Contains(s As String) As Boolean
      Return s.Contains(_compareTo)
   End Function

   Function StartsWith(s As String) As Boolean
      Return s.StartsWith(_compareTo)
   End Function

End Class

Usage:

Dim result As String() = Array.FindAll(arr, New ArrayComparer("Ra").Contains)

Answer 5

VB

Dim arr() As String = {"ravi", "Kumar", "Ravi", "Ramesh"}
Dim result = arr.Where(Function(a) a.Contains("ra")).Select(Function(s) Array.IndexOf(arr, s)).ToArray()

C#

string[] arr = { "ravi", "Kumar", "Ravi", "Ramesh" };
var result = arr.Where(a => a.Contains("Ra")).Select(a => Array.IndexOf(arr, a)).ToArray();

-----Detailed------

Module Module1

    Sub Main()
        Dim arr() As String = {"ravi", "Kumar", "Ravi", "Ramesh"}
        Dim searchStr = "ra"
        'Not case sensitive - checks if item starts with searchStr
        Dim result1 = arr.Where(Function(a) a.ToLower.StartsWith(searchStr)).Select(Function(s) Array.IndexOf(arr, s)).ToArray
        'Case sensitive - checks if item starts with searchStr
        Dim result2 = arr.Where(Function(a) a.StartsWith(searchStr)).Select(Function(s) Array.IndexOf(arr, s)).ToArray
        'Not case sensitive - checks if item contains searchStr
        Dim result3 = arr.Where(Function(a) a.ToLower.Contains(searchStr)).Select(Function(s) Array.IndexOf(arr, s)).ToArray
        Stop
    End Sub

End Module

Answer 6

In case you were looking for an older version of .NET then use:

Module Module1

    Sub Main()
        Dim arr() As String = {"ravi", "Kumar", "Ravi", "Ramesh"}
        Dim result As New List(Of Integer)
        For i As Integer = 0 To arr.Length
            If arr(i).Contains("ra") Then result.Add(i)
        Next
    End Sub

End Module