📜Recap

Types

5 collections including 4 functional/immutable

List: default choice / Versatile, Practical → [ ], Operators: Cons ::, Append @, Pattern matching

Array: fixed-size, mutable, performance-oriented (e.g. indexer) → [| |] less handy to write than [ ]

Seq: deferred evaluation (Lazy), infinite sequence

Set: unique elements

Map: values by unique key

API

Rich → Hundreds of functions >> Fifty for LINQ

Consistency → Common syntax and functions → Functions preserve the collection type (≠ LINQ sticked to IEnumerable<>)

Semantic → Function names closer to JS

Comparison C♯, F♯, JavaScript

C♯ LINQ	F♯	JS Array
Select(), SelectMany()	map, collect	map(), flatMap()
Any(predicate), All()	exists, forall	some(), every()
Where(), ×	filter, choose	filter(), ×
First(), FirstOrDefault()	find, tryFind	×, find()
×	pick, tryPick	×
Aggregate([seed]])	fold, reduce	reduce()
Average(), Sum()	average, sum	×
ToList(), AsEnumerable()	List.ofSeq, toSeq	×
Zip()	zip	×

BCL types

• Array

• ResizeArray for C# List

• Dictionaries: dict, readOnlyDict

For interop or performance

🕹️ Exercises

On Exercism.io / F# track

Exercise	Level	Topics
High Scores	Easy	List
Protein Translation	Medium+	Seq/List 💡
ETL	Medium	Map of List, Tuple
Grade School	Medium+	Map of List

☝ Pre-requisites: → Create an account, with GitHub for instance → Solve the first exercises to unlock the access to the one above

💡 Tips: → string is a Seq<char> → What about Seq.chunkBySize?

🔗 Additional resources

• All functions, with their cost in O(?)

• Choosing between collection functions, F# for fun and profit (2015)

• An F# Primer for curious C# developers - Work with collections, 2020

• Formatage des collections