两个 arrays 在多个 arrays 中的交集

Question

I'm searching for a way for extracting common values in at least two arrays in the list of arrays in JS.

eg [["google", "amazon", "reddit"], ["telegram", "reddit", "discord"], ["firefox", "telegram", "chrome"]] to ["reddit", "telegram]

The point is 1. the arrays can be any length 2. common at least two (or any specified number) of arrays but not all of the arrays.

I looked a countless numbers of SO posts and also looked the lodash functions, they are all talking either "of two arrays" or "of all arrays from multiple arrays", none of them were takling "of two/arbitrary arrays from multiple arrays". So I'm here to ask.

Thanks.

Answer 1

 let arr = [["google", "amazon", "reddit"], ["telegram", "reddit", "discord"], ["firefox", "telegram", "chrome"]] const flatedArr =arr.flat(Infinity); const repeatedItems = [] const nonRepeatedItems = [] flatedArr.forEach(val => { if(nonRepeatedItems.includes(val)) return repeatedItems.push(val) return nonRepeatedItems.push(val) }) console.log(repeatedItems); // ["reddit","telegram"]

Answer 2

Here is an O(n) version using Map to not bother about the type of the values

Note this will also return dupes in one array

 const extractCommonValues = arr => { const counts = arr.flat().reduce((acc, cur) => (acc.set(cur, (acc.get(cur) || 0) + 1), acc), new Map()); return [...counts.keys()].filter(el => counts.get(el) > 1); }; console.log( extractCommonValues([["google", "amazon", "reddit"], ["telegram", "reddit", "discord"], ["firefox", "telegram", "chrome"]]) ) // will extract the dupe amazon in the first array console.log( extractCommonValues([["google", "amazon", "reddit", "amazon"], ["telegram", "reddit", "discord"], ["firefox", "telegram", "chrome"]]) )

To ignore dupes in the sub arrays we can set them first

 const extractCommonValues = arr => { const counts = arr.map(subArr => [...new Set(subArr)]).flat().reduce((acc, cur) => (acc.set(cur, (acc.get(cur) || 0) + 1), acc), new Map()); return [...counts.keys()].filter(el => counts.get(el) > 1); }; console.log( extractCommonValues([["google", "amazon", "reddit", "amazon"], ["telegram", "reddit", "discord"], ["firefox", "telegram", "chrome"]]) )

Answer 3

using various Array methods, and Set , it can be accomplished fairly easily

 const input = [["google", "amazon", "reddit"], ["telegram", "reddit", "discord"], ["firefox", "telegram", "chrome"]]; // remove duplicaates within a sub array const uniqueInSub = input.map(_=>[...new Set(_)]); // create a list of all values in a flat array const uniqueInSubFlat = uniqueInSub.flat(); // list of unique values const values = [...new Set(uniqueInSubFlat)]; // array of [value, count] pairs const pre1 = values.map(value => [ value, uniqueInSubFlat.filter(subValue => subValue === value).length]); // value,count pairs where the count > 1 and < the number of sub arrays const pre2 = pre1.filter(([, count]) => count > 1 && count < input.length); // array of values const result = pre2.map(([value])=>value); console.log(result);

Answer 4

 function findCommonValues(arrays, minCommon) { // Create an object to keep track of the count of each value const countMap = new Map(); // Iterate over each array for (const array of arrays) { // Iterate over each value in the array for (const value of array) { // Increment the count for the current value countMap.set(value, (countMap.get(value) || 0) + 1); } } // Filter the values that have a count equal to or greater than the specified minimum const commonValues = []; for (const [value, count] of countMap.entries()) { if (count >= minCommon) { commonValues.push(value); } } return commonValues; } // Example usage const arrays = [ ["google", "amazon", "reddit"], ["telegram", "reddit", "discord"], ["firefox", "telegram", "chrome"] ]; const commonValues = findCommonValues(arrays, 2); console.log(commonValues); // Output: ["reddit", "telegram"]

Answer 5

You could use .flat() and .filter() methods as follows:

 const data = [["google", "amazon", "reddit"], ["telegram", "reddit", "discord"], ["firefox", "telegram", "chrome"]], common = [...new Set(data.flat().filter((v,i,a) => a.filter(val => val === v).length > 1))]; console.log( common );

Or More efficiently....

 const data = [["google", "amazon", "reddit"], ["telegram", "reddit", "discord"], ["firefox", "telegram", "chrome"]], all = data.flat(), uniq = [...new Set(all)], common = uniq.filter(v => all.filter(val => val === v).length > 1); console.log( common );