# Using the let keyword in .NET LINQ to store variables within a statement

April 20, 2017 Leave a comment

It happens that we have a LINQ statement where we want to refer to partial results by variable names while expressing some computation. The “let” keyword lets us do that. Those who are familiar for the F# language already know that “let” is an important keyword to bind some value to a variable.

Suppose we have the following list of integers:

List<int> integers = new List<int>() { 5, 7, 4, 6, 10, 4, 6, 4, 5, 12 };

…and we want to calculate the following:

- The sum of the first and last elements in the list, i.e. 5 + 12 = 17
- The product of the minimum and maximum integers, i.e. 4 * 12 = 48
- Add these two partial results and return this sum as the final result of the computation, i.e. 48 + 17 = 65

Don’t look for any rationale behind this computation, it’s just an easy example for demonstration purposes.

LINQ is flexible so there are multiple ways to solve this problem. A single statement using the two partial results may look like the following:

int computationResult = (from i in integers let sumOfFirstAndLast = integers[0] + integers[integers.Count - 1] let productOfMinAndMax = (integers.Max() * integers.Min()) select sumOfFirstAndLast + productOfMinAndMax).First();

Of course we could have eliminated the variables “sumOfFirstAndLast” and “productOfMinAndMax” as follows:

int computationResultAlt = (from i in integers select integers[0] + integers[integers.Count - 1] + (integers.Max() * integers.Min())).First();

…but I think the first solution allows breaking up a potentially long select clause into more “digestible” pieces.

You can view all LINQ-related posts on this blog here.