Some Common Operations using List <string>

Some Common Operations using List - Part I

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Posted by: Suprotim Agarwal, on 1/15/2010, in category "LINQ"
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Abstract: In this article, I will demonstrate some common operations on List using LINQ

Some Common Operations using List<string> - Part I

I have been writing some articles in the past where I try and demonstrate the capabilities of LINQ using some common examples. Some of these articles are:

Some Common Operations using LINQ To XML - Part I

Some Common Operations using LINQ To XML - Part II

Some Common Operations using LINQ To XML - Part III

Some Common GroupBy Operations on List<> using LINQ

In this article and the next one, I will demonstrate some common operations on List<string> using LINQ. I assume that you are familiar with LINQ.

Here are the sample List<string> for demonstration purposes. The VB.NET code has been converted using a conversion tool and accuracy has not been tested.

List<string> lstOne = new List<string>() { "January", "February", "March"};

List<string> lstTwo = new List<string>() { "January", "April", "March"};

List<string> lstThree = new List<string>() { "January", "April", "March", "May" };

List<string> lstFour = new List<string>() { "Jan", "Feb", "Jan", "April", "Feb" };

IEnumerable<string> lstNew = null;

VB.NET

Dim lstOne As New List(Of String) (New String() {"January", "February", "March"})

Dim lstTwo As New List(Of String) (New String() {"January", "April", "March"})

Dim lstThree As New List(Of String) (New String() {"January", "April", "March", "May"})

Dim lstFour As New List(Of String) (New String() {"Jan", "Feb", "Jan", "April", "Feb"})

Dim lstNew As IEnumerable(Of String) = Nothing

We will be printing the results on the console using a simple method shown here:

static void PrintList(IEnumerable<string> str)

{

foreach (var s in str)

Console.WriteLine(s);

Console.WriteLine("-------------");

}

VB.NET

Shared Sub PrintList(ByVal str As IEnumerable(Of String))

For Each s In str

Console.WriteLine(s)

Console.WriteLine("-------------")

End Sub

Let us get started.

1. Display common elements between two List<string>

Use the Enumerable.Intersect method

// Compare two List<string> and display common elements

lstNew = lstOne.Intersect(lstTwo, StringComparer.OrdinalIgnoreCase);

PrintList(lstNew);

VB.NET

lstNew = lstOne.Intersect(lstTwo, StringComparer.OrdinalIgnoreCase)

PrintList(lstNew)

OUTPUT

2. Display elements found in one List<string> but not in the other

Use the Enumerable.Except method

// Compare two List<string> and display items of lstOne not in lstTwo

lstNew = lstOne.Except(lstTwo, StringComparer.OrdinalIgnoreCase);

PrintList(lstNew);

VB.NET

lstNew = lstOne.Except(lstTwo, StringComparer.OrdinalIgnoreCase)

PrintList(lstNew)

Note: The StringComparer.OrdinalIgnoreCase performs a case-insensitive ordinal string comparison

OUTPUT

3. Display distinct elements from a List<string>

Use the Enumerable.Distinct method

// Unique List<string>

lstNew = lstFour.Distinct(StringComparer.OrdinalIgnoreCase);

PrintList(lstNew)

VB.NET

lstNew = lstFour.Distinct(StringComparer.OrdinalIgnoreCase)

PrintList(lstNew)

OUTPUT

4. Convert all elements of a List<string> to UpperCase

Use the List.ConvertAll method

// Convert elements of List<string> to Upper Case

lstNew = lstOne.ConvertAll(x => x.ToUpper());

PrintList(lstNew);

VB.NET

lstNew = lstOne.ConvertAll(Function(x) x.ToUpper())

PrintList(lstNew)

OUTPUT

5. Concatenate and Sort two List<string>

Use the Enumerable.Concat method

// Concatenate and Sort two List<string>

lstNew = lstOne.Concat(lstTwo).OrderBy(s => s);

PrintList(lstNew);

VB.NET

lstNew = lstOne.Concat(lstTwo).OrderBy(Function(s) s)

PrintList(lstNew)

OUTPUT

6. Concatenate Unique Elements of two List<string>

Use the Enumerable.Concat and Enumerable.Distinct method

// Concatenate Unique Elements of two List<string>

lstNew = lstOne.Concat(lstTwo).Distinct();

PrintList(lstNew);

VB.NET

lstNew = lstOne.Concat(lstTwo).Distinct()

PrintList(lstNew)

OUTPUT

7. Reverse a List<string>

Use the List.Reverse method

// Reverse a List<string>

lstOne.Reverse();

PrintList(lstOne);

VB.NET

lstOne.Reverse()

PrintList(lstOne)

OUTPUT

8. Search a List<string> and Remove the Search Item from the List<string>

Use the List.RemoveAll method

// Search a List<string> and Remove the Search Item

// from the List<string>

int cnt = lstFour.RemoveAll(x => x.Contains("Feb"));

Console.WriteLine("{0} items removed", cnt);

PrintList(lstFour);

VB.NET

Dim cnt As Integer = lstFour.RemoveAll(Function(x) x.Contains("Feb"))

Console.WriteLine("{0} items removed", cnt)

PrintList(lstFour)

OUTPUT

So these were some common List<string> operations. In the next article[UPDATE: The article is online Some Common Operations using List<string> - Part II], we will see some more advanced operations on the List<string>. Stay tuned! The entire source code of this article can be downloaded over here

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