Functional programming with Linq – IEnumerable.Aggregate

As I was learning functional programming with F# I came across the List.reduce function which iterates through a list and builds up an accumulator value by running another function against each element in the list.

Back to the more familiar C# territory, LINQ has introduced some functional features to C# and one of these is the Aggregate function on IEnumerable<T> which works in the same way as the List.reduce function.

In the following example, you can use the Aggregate function to built up a comma separated string from an array of string:

var strings = new List<string> { "Jack", "Jill", "Jim", "Joe", "Jane" };
// this returns "Jack, Jill, Jim, Joe, Jane"
var comSeparatedStrings = strings.Aggregate((acc, item) => acc + ", " + item);


Yan Cui

I’m an AWS Serverless Hero and the author of Production-Ready Serverless. I have run production workload at scale in AWS for nearly 10 years and I have been an architect or principal engineer with a variety of industries ranging from banking, e-commerce, sports streaming to mobile gaming. I currently work as an independent consultant focused on AWS and serverless.

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