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In this article Xiaobian introduces in detail "JavaScript how to find repeating or non-repeating elements in the array", detailed content, clear steps, and proper handling of details. I hope that this article "JavaScript how to find repeating or non-repetitive elements in the array" can help you solve your doubts.

1. Repeat elements or non-repeating elements in the array

Double cycle + slice to find out the duplicate elements. Although you are only required to find the repeating elements, you should be careful to remove the duplicates by the way, otherwise the outer loop will check the repeating elements again; use flag to record the number of repeats and put the elements into the new array only on the first repetition

Function search (arr) {let res = [] let flag = 0 for (let I = 0 position I

< arr.length;i++){ for(let j = i+1;j item[1] >

1) .map (item = > item [0]) / / find non-repeating elements That is, the number of occurrences is equal to 1 return [... map.entries ()] .filter (item = > item [1] = = 1) .map (item = > item [0]) / / find out the element return [... map.entries ()] .filter (item = > item [1] = = Math.max (... filter () .map (item = > item [0])} two, array flattening / array dimensionality reduction

A two-dimensional array, taking [[], [{adrug 1}], [], [3pr 4], 5] as an example, gets [{aburel 1}, 3pr 4pr 5] after dimension reduction.

Two-dimensional array: double loop

You need to check whether each element is an array

Function flatten (arr) {const res = [] for (let I = 0 I)

< arr.length; i++){ if(Array.isArray(arr[i])){ for(let j = 0;j < arr[i].length;j++){ res.push(arr[i][j]) } } else { res.push(arr[i]) } } return res}二维数组：循环 + concat concat 本身就可以给数组降维一次 function reduceDiemension(arr){ const res = [] for(let i = 0;i < arr.length;i++){ res = res.concat(arr[i]) } return res}二维数组：reduce + concat 上面的过程本身是一种归并，所以考虑使用 reduce function flatten(arr){ return arr.reduce((acc,cur) =>

Acc.concat (cur), [])} 2D array: expand / apply + concat

Convert the array to a parameter list by expanding the original array or using it as the second parameter of apply

Function flatten (arr) {/ / return [] .concat ([], arr) return [] .concat (... arr)}

Multidimensional array, take the following array as an example:

Const arr = [

one,

[

2, [3]

[4,5,6]

[7,8,9]

10,11

]

twelve,

thirteen,

[15,16,17]

]

[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 15, 16, 17]

Multidimensional array: toString + split

Array dimensionality reduction can be seen as removing all parentheses, and the toString method of the array can just do this, and then call the split of the string to convert the string back to the array. However, this approach is limited and requires that the data types of array elements are all the same.

Function flattern_numberArray (arr) {return arr.toString () .split (",") .map (x = > Number)} Multidimensional array: forEach + Recursive function flatten (arr) {const res = [] arr.forEach (item = > {if (Array.isArray (item)) {flatten (item)} else {res.push (item)}) return res} Multidimensional Array: reduce + Recursive

Similarly, the above process is a merge that can be done using reduce. It is important to note that the callback function of reduce must return an array, so stop using push

Function flatten (arr) {return arr.reduce ((acc,cur) = > {if (Array.isArray (cur)) {return [... acc,... flatten (cur)]} else {return [... acc,cur]}, [])} Multidimensional array: while + some

As long as there is an array in the array, use concat to reduce the dimension of the array. This method does not use recursion.

Function flatten (arr) {while (arr.some (item = > Array.isArray (item) {arr = [] .concat (... arr)} return arr} an array of uncertain dimensions: flat

Array dimensionality reduction, directly using the previously mentioned flat is the easiest. Pass parameter 1 by default, which means one dimension reduction; you can pass parameter Infinity to achieve complete dimension reduction, and finally get an one-dimensional array.

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