使用for循环从数组中拼接多个元素

Question

I want to splice some multiple index of array here is my code example :

  let arrayA = ["aa","bb","cc","dd","ee","ff","gg","hh"]; let arrrayIndexSplice = [0,1,3]; let test = null; for (let i of arrrayIndexSplice) { test = arrayA.splice(i,1); } console.log(arrayA); 

expected result is ["cc","ee","ff","gg","hh"];

actual result is ["bb", "dd", "ee", "gg", "hh"]

Answer 1

When splicing out the index of all following values gets decreased. Therefore splice out the last first:

let arrrayIndexSplice = [0, 1, 3];
for (let i of arrrayIndexSplice.sort().reverse()) {
 arrayA.splice(i, 1);
}

Or just filter:

 arrayA = arrayA.filter((_, i) => !arrayIndexSplice.includes(i));

Answer 2

you should start from ending means i-- let's try following

let arrayA=["aa","bb","cc","dd","ee","ff","gg","hh"];
let arrrayIndexSplice=[0,1,3];
for (let i=arrrayIndexSplice.length-1;i>=0;i--){arrayA.splice(arrrayIndexSplice[i],1)}

Answer 3

The problem may be that you are traversing the array in ascending order. So when you splice the first element, index of other elements change. Negative iteration on array may help.

let arrayA=["aa","bb","cc","dd","ee","ff","gg","hh"];
let arrrayIndexSplice=[0,1,3];
for (let i=arrrayIndexSplice.length-1; i > -1; i--){arrayA.splice(i,1)}

Answer 4

You can filter out all the elements with indexes you want to exclude.

 let arrayA = ["aa", "bb", "cc", "dd", "ee", "ff", "gg", "hh"]; let arrrayIndexSplice = [0, 1, 3]; arrayA = arrayA.filter((item, index)=> !arrrayIndexSplice.includes(index)); console.log(arrayA); 

Answer 5

My idea is to replace the items in that index with a special character or string and then remove that special character or string using replace again:

 let arrayA = ["aa", "bb", "cc", "dd", "ee", "ff", "gg", "hh"]; let arrrayIndexSplice = [0, 1, 3]; let test = null; arrayA.forEach((val, index) => { if(arrrayIndexSplice.includes(index)){ arrayA[index] = '##'; } }); arrayA = arrayA.join(',').replace(/##,/g, '').split(','); console.log(arrayA); 

Answer 6

While you traverse through the for of loop you are constantly changing the array itself and so the indices are shifted to the right every loop step

Your example

arrayA: ["aa", "bb", "cc", "dd", "ee", "ff", "gg", "hh"]
// start loop
// 1st iteration
// test = arrayA.splice(i,1);
test = 0
arrayA = ["bb", "cc", "dd", "ee", "ff", "gg", "hh"]  // index 0 removed

// 2nd iteration
// test = arrayA.splice(i,1);
test = 1
arrayA = ["bb", "dd", "ee", "ff", "gg", "hh"]  // index 1 removed

// 3rd iteration
// test = arrayA.splice(i,1);
test = 3
arrayA = ["bb", "dd", "ee", "gg", "hh"]  // index 3 removed

This works: You need to get the index of the current arrrayIndexSplice element, so you can decrease the splice start index by that amount

 console.clear() let arrayA = ["aa", "bb", "cc", "dd", "ee", "ff", "gg", "hh"]; let arrrayIndexSplice = [0, 1, 3]; for (let k in arrrayIndexSplice) { if (arrrayIndexSplice.hasOwnProperty(k)) { arrayA.splice(arrrayIndexSplice[k]-k, 1) } } console.log(arrayA) 

This also works: It doesn't work with a loop, but a filter function

 let arr = ["aa", "bb", "cc", "dd", "ee", "ff", "gg", "hh"]; let indices = [0,1,3] function filterIndices(arr, indices, swap = false) { return arr.filter((item, index, source) => { return swap ? !indices.includes(index) : indices.includes(index); }) } newArr = filterIndices(arr, indices, true) console.log(newArr) 

Answer 7

You can use below code :

let arrayA = ["aa", "bb", "cc", "dd", "ee", "ff", "gg", "hh"];
let arrrayIndexSplice = [0, 1, 3];
for (let i of arrrayIndexSplice.length) {
  arrayA.splice(arrrayIndexSplice[i], 1)
}