C# List ConvertAll

last modified July 5, 2023

In this article we show how to convert list elements into another type in C# using the ConvertAll method.

C# list is a collection of elements of the same type. The elements can be accessed by index.

public List<TOutput> ConvertAll<TOutput> (Converter<T,TOutput> converter);

TOutput is the type of the elements of the target list. Converter is a delegate that converts each element from one type to another type.

The method returns a list of the target type containing the converted elements from the source list. The elements of the source list are not modified.

C# List convert ints to decimals

In the next example, we use ConvertAll to convert a list of integers into a list of decimals.

var vals = new List<int> { 1, 2, 3, 4, 5 };

List<decimal> res = vals.ConvertAll((e) => (decimal)e);
Console.WriteLine(vals[0].GetType());
Console.WriteLine(res[0].GetType());

We define a list of integers. From the list we generate a new list where the source elements are converted into decimals.

List<decimal> res = vals.ConvertAll((e) => (decimal)e);

We pass the ConvertAll method a lambda expression, where we cast the integer values into decimals.

Console.WriteLine(vals[0].GetType());
Console.WriteLine(res[0].GetType());

With GetType, we determine the type of the first element of the source and target lists.

$ dotnet run
System.Int32
System.Decimal

C# list convert words to word lengths

In the next example, we use the ConvertAll method to convert a list of strings into a list of string lengths.

var words = new List<string> { "sky", "kanoe", "cannon", "war", "falcon"};
var wlens = words.ConvertAll((e) => e.Length);

Console.WriteLine(string.Join(",", words));
Console.WriteLine(string.Join(",", wlens));

We assume that we work only with ASCII characters.

var words = new List<string> { "sky", "kanoe", "cannon", "war", "falcon"};

We have a list of words.

var wlens = words.ConvertAll((e) => e.Length);

The converter is a lambda expression which invokes the Length property on each list element.

$ dotnet run
sky,kanoe,cannon,war,falcon
3,5,6,3,6

C# list rounding elements

In the next example, we round the elements of a list.

var vals = new List<double> { 1.33, 2.27, 3.16, 4.93, 5.44 };

var res = vals.ConvertAll((e) => double.Round(e, 1, 
    MidpointRounding.AwayFromZero));

Console.WriteLine(string.Join(",", vals));
Console.WriteLine(string.Join(",", res));

We define a list of double values. The values are rounded.

var res = vals.ConvertAll((e) => double.Round(e, 1, 
    MidpointRounding.AwayFromZero));

For rounding, we use the MidpointRounding.AwayFromZero mode.

$ dotnet run
1.33,2.27,3.16,4.93,5.44
1.3,2.3,3.2,4.9,5.4

Source

List ConvertAll method

In this article we have showed how to convert list elements in C# with ConvertAll.

Author

My name is Jan Bodnar and I am a passionate programmer with many years of programming experience. I have been writing programming articles since 2007. So far, I have written over 1400 articles and 8 e-books. I have over eight years of experience in teaching programming.

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