Apply lambda expression for specific indices in list c#

Question

I am new to lambda expression and I have problem to convert parts of code which involves indices of list inside the loop to equivalent lambda expression.

Example 1: Working with different indices inside one list

List<double> newList = new List<double>();
for (int i = 0; i < list.Count - 1; ++i)
{
     newList.Add(list[i] / list[i + 1]);
}

Example 2: Working with indices from two lists

double result = 0;
for (int i = 0; i < list1.Count; ++i)
{
    result += f(list1[i]) * g(list2[i]);
}

How to write equivalent lambda expressions?

Answer 1

A lambda expression is something that looks like {params} => {body}, where the characteristic symbol is the => "maps to." What you are asking for are typically referred to as LINQ query expressions, which come in two styles:

• The functional style of query is typically a sequence of chained calls to LINQ extension methods such as Select, Where, Take, or ToList. This is the style I have used in the examples below and is also the much-more prevalent style (in my experience).

• The "language integrated" style (*) uses built-in C# keywords that the compiler will turn into the functional style for you. For example:

  var query = from employee in employeeList
              where employee.ManagerId == 17
              select employee.Name;
  
                  | compiler
                  v rewrite
  
  var query = employeeList
      .Where(employee => employee.ManagerId == 17)
      .Select(employee => employee.Name);
  

Example 1:

var newList = Enumerable.Range(0, list.Count - 1)
    .Select(i => list[i] / list[i + 1])
    .ToList();

Example 2:

var result = Enumerable.Zip(list1.Select(f), list2.Select(g), (a, b) => a * b).Sum();

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(*) I'm not actually sure this is the official name for it. Please correct me with the proper name if you know it.