Reputation: 1040
I have an array [a, b, c]
. I want to be able to insert a value between each elements of this array like that: [0, a, 0, b, 0, c, 0]
.
I guess it would be something like this, but I can't make it works.
for (let i = 0; i < array.length; i++) {
newArray = [
...array.splice(0, i),
0,
...array.splice(i, array.length),
];
}
Thank you for helping me!
Upvotes: 35
Views: 30130
Reputation: 1513
A fast solution not in-place: (based on my >10x flatMap (similar use-case))
function arrayJoin(inp, sep) {
let tar = new Array(inp.length * 2 + 1)
for (let i = inp.length - 1; i > -1; --i) {
tar[i * 2 + 1] = inp[i]
tar[i * 2] = sep
}
tar[inp.length * 2] = sep
return tar
}
// Verify
let inp = arrayJoin(["a", "b", "c"], 0)
console.log(inp.join(" "))
If you need modification (in-place) use the while {splice}
approach
Upvotes: 0
Reputation: 71
Thanks for your question and thanks to all contributors, for their answers. This would be my approach
const arr = ["a", "b", "c"];
let toAdd = 0;
for (let i = 0; i <= arr.length; i += 2) {
arr.splice(i, 0, toAdd);
}
console.log(arr);
or
const arr = ["a", "b", "c"];
let toAdd = 0;
const newArr = [];
newArr.unshift(toAdd);
for (let i = 0; i < arr.length; i++) {
newArr.push(arr[i]);
newArr.push(toAdd);
}
console.log(newArr);
Cheers Nav
Upvotes: 0
Reputation: 776
I think this is correct, ie, just adds the element between the elements of the array, and should be pretty efficient:
const intersperse = ([first, ...tail]: any[], element: any) => (
(first === undefined) ? [] : [first].concat(...tail.map((e) => [element, e]))
);
console.log(intersperse([], 0));
console.log(intersperse([1], 0));
console.log(intersperse([1, 2, 3], 0));
Upvotes: 0
Reputation: 10522
Straight forward way of inserting only between:
const arr = ['a', 'b', 'c'];
arr.map((v, i) => !i || i === arr.length - 1 ? [v] : [0, v]).flat()
Upvotes: 0
Reputation: 297
You can try with the below code. It will add 0 in middle of each two element of the array
console.log(['a', 'b', 'c'].reduce((r, a) => r.concat(a,0), [0]).slice(1, -1))
Upvotes: 2
Reputation: 2424
If you want to insert elements only after existing ones:
console.log(["a", "b", "c"].map(i => [i, 0]).flat())
Upvotes: 1
Reputation: 1267
Another way is to use some functional methods like zip and flat. Check out lodash.
const array = ['a', 'b', 'c']
const zeros = Array(array.length + 1).fill(0)
const result = _.zip(zeros, array).flat().filter(x => x !== undefined)
console.log(result)
<script src="https://cdn.jsdelivr.net/npm/[email protected]/lodash.min.js"></script>
Upvotes: 0
Reputation: 2858
all of the above methods in very long strings made my android computer run on React Native go out of memory. I got it to work with this
let arr = ['a', 'b', 'c'];
let tmpArr = [];
for (const item in arr) {
tmpArr.push(item);
tmpArr.push(0);
}
console.log(tmpArr);
Upvotes: 0
Reputation: 4551
Another ES6+ version using flatmap (if creation of a new array instead is ok):
['a', 'b', 'c', 'd']
.flatMap((e, index) => index ? [e, 0] : [0, e, 0])
Upvotes: 7
Reputation: 53229
let arr = ['a', 'b', 'c'];
function insert(items, separator) {
const result = items.reduce(
(res, el) => [...res, el, separator], [separator]);
return result;
}
console.log(insert(arr, '0'));
Upvotes: 0
Reputation: 475
Another way if you want to exclude the start and end of array is :
var arr = ['a', 'b', 'c']
var newArr = [...arr].map((e, i) => i < arr.length - 1 ? [e, 0] : [e]).reduce((a, b) => a.concat(b))
console.log(newArr)
Upvotes: 17
Reputation: 386883
For getting a new array, you could concat the part an add a zero element for each element.
var array = ['a', 'b', 'c'],
result = array.reduce((r, a) => r.concat(a, 0), [0]);
console.log(result);
Using the same array
var array = ['a', 'b', 'c'],
i = 0;
while (i <= array.length) {
array.splice(i, 0, 0);
i += 2;
}
console.log(array);
A bit shorter with iterating from the end.
var array = ['a', 'b', 'c'],
i = array.length;
do {
array.splice(i, 0, 0);
} while (i--)
console.log(array);
Upvotes: 27
Reputation: 26201
This looks like the intersperse algorithm but does some addition to the head and tail as well. So i call it extrasperse
.
var arr = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9],
extrasperse = (x,a) => a.reduce((p,c,i) => (p[2*i+1] = c, p), Array(2*a.length+1).fill(x));
console.log(JSON.stringify(extrasperse("X",arr)));
Upvotes: 0
Reputation: 200
It could be done with strings by splitting and joining.
var arr = ['a', 'b', 'c'];
var newArray = ("0," + arr.toString().split(",").join(",0,")).split(",");
console.log(newArray);
Upvotes: 0
Reputation: 168
Another way:
var a = ['a', 'b', 'c'],
b;
b = a.reduce((arr, b) => [...arr, b, 0], []);
console.log(b);
Upvotes: 4
Reputation: 101778
You could use .reduce()
:
function intersperse(arr, val) {
return arr.reduce((acc, next) => {
acc.push(next);
acc.push(val);
return acc;
}, [val]);
}
console.log(intersperse(['a', 'b', 'c'], 0));
Or to accomplish this by modifying the original array:
function intersperse(arr, val) {
for (let i = 0; i <= arr.length; i += 2) {
arr.splice(i, 0, val);
}
return arr;
}
console.log(intersperse(['a', 'b', 'c'], 0));
Upvotes: 3
Reputation: 122155
You can use map()
with ES6 spread syntax and concat()
var arr = ['a', 'b', 'c']
var newArr = [0].concat(...arr.map(e => [e, 0]))
console.log(newArr)
Upvotes: 9
Reputation: 31712
function insert(arr, elm) {
var newArr = [];
for(var i = 0; i < arr.length; i++) { // for each element in the array arr
newArr.push(elm); // add the new element to newArr
newArr.push(arr[i]); // add the current element from arr
}
newArr.push(elm); // finally add the new element to the end of newArr
return newArr;
}
console.log(insert(["a", "b", "c"], 0));
Upvotes: 0
Reputation: 32175
You just need to loop over the array elements and add the new element in each iteration, and if you reach the last iteration add the new element after the last item.
This is how should be your code:
var arr = ['a', 'b', 'c'];
var results = [];
arr.forEach(function(el, index) {
results.push(addition);
results.push(el);
if (index === arr.length - 1)
results.push(addition);
});
Demo:
This is a Demo snippet:
var arr = ['a', 'b', 'c'];
var results = [];
var addition = 0;
arr.forEach(function(el, index) {
results.push(addition);
results.push(el);
if(index === arr.length -1)
results.push(addition);
});
console.log(results);
Upvotes: 1
Reputation: 10458
You could do
let arr = ['a', 'b', 'c'];
arr = arr.reduce((a, b) => {
a.push(0);
a.push(b);
return a;
}, []);
arr.push(0);
console.log(arr);
Upvotes: 0