Set intersection

As explained in Secrets of the JavaScript Ninja, Second Edition

A set operation that produces a set containing the elements common to the operand sets.

const ninjas = new Set(["Kuma", "Hattori", "Yagyu"]);         
const samurai = new Set(["Hattori", "Oda", "Tomoe"]);       

const ninjaSamurais = new Set(
  [...ninjas].filter(ninja => samurai.has(ninja))                 #A
);

assert(ninjaSamurais.size === 1, "There's only one ninja samurai");
assert(ninjaSamurais.has("Hattori"), "Hattori is his name");

How Secrets of the JavaScript Ninja, Second Edition covers it

How deep it goes

Defines the common-elements result and demonstrates an implementation using spread, filter(), and has().

Examples

Demonstrates intersecting ninja and samurai Sets, yielding Hattori as the sole shared member.

What it assumes

Assumes familiarity with JavaScript Sets, arrays, filter(), and spread syntax; does not build those features from scratch.

What you can do after

Build an intersection by filtering one Set’s values with the other Set’s has() method and wrapping the matches in a new Set.

How it connects

Connects Set intersection to array conversion with spread syntax and filtering with Array.filter().

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Also explained in

• 

  liveBookmanning.com
  Advanced Algorithms and Data StructuresAn edge intersection is a geometric point or region at which two drawn graph edges meet away from their permitted common endpoint.
• 

  liveBookmanning.com
  Geometry for ProgrammersA geometric or set operation whose result consists of elements shared by the combined objects.
• 

  liveBookmanning.com
  Julia as a Second LanguageSet intersection is the operation that produces the elements shared by two or more sets.
• 

  liveBookmanning.com
  Python How-ToSet intersection is the operation that produces the elements common to two sets or set-compatible collections.

Compare how 5 books explain set intersection →

Related concepts

• setuses · A set is a collection of unique elements in which membership is determined by whether an element is present, not by duplicate occurrences.
• set operationkind of · A set operation combines, compares, or transforms sets according to the membership of their elements.
• set differencecontrasts with · Set difference is the set of elements that belong to one set but not to another.
• inner joinequivalent to · An inner join is a relational operation that returns combinations of rows only when the join condition matches records in both input relations.

This explainer was generated by Manning's knowledge graph from the text of Secrets of the JavaScript Ninja, Second Edition. The section links point to the parts of the book it draws on.