Java Script - add null value to array if element is not present at specific index
Array length is 7
Original array
var arr = [2, 4, 6];
Required array
arr = [null,null,2,null,4,null,6];
- 0 is not in the array, so you need to replace it with a zero value,
- 1 cannot be replaced with zero and
- 2 is available so to put 2 into a new array, and so on.
I'll write longevity for all the answers soon.
function createArrayFromArray(array, length) {
var new_array = new Array(length);
for (var i = 0; i < new_array.length; i++) {
new_array[i] = null;
}
for (var i = 0; i < array.length; i++) {
new_array[array[i]] = array[i];
}
return new_array;
}
console.log(createArrayFromArray(arr, 7)); //[null, null, 2, null, 4, null, 6]
You can use method splice()
for array
var arr=[2,4,6];
var l = arr[arr.length-1];
for(var i=0; i<=l; i++){
if(arr[i] !== i){
arr.splice(i, 0, null);
}
}
Output: [null, null, 2, null, 4, null, 6]
This changes the original array.
You just have to find the maximum value in the array and then loop over from 0 to that max value, checking each value to see if it is present in the source or not:
var arr = [2, 4, 6];
var max = Math.max.apply(Math, arr);
var result = [];
for (var i = 0; i <= max; i++) {
if (arr.indexOf(i) !== -1) {
result[i] = i;
} else {
result[i] = null;
}
}
Working demo: http://jsfiddle.net/jfriend00/c7p8mkqy/
As I said in my comments, I would like to know what problem you are trying to solve, because it seems that both the original and the newly created data structure are inefficient structures that can probably use different forms of data and work more efficiently. ... But we can only help you make smarter choices if you explain the actual problem, not just your solution.
Considering that you have only one input arr
that you want to fill inside. Try the following:
var arr = [2, 4, 6];
var output = [];
while (arr.length>0){
var first = arr.splice(0,1);
while (output.length<first[0])
output.push(null);
output.push(first[0]);
}
// output should be [null,null,2,null,4,null,6];
Try:
var arr = [2, 4, 6];
var new_arr = [];
var i = 0;
while(i < 7){
var pos = arr.indexOf(i++);
new_arr.push(pos !== -1 ? arr[pos] : null)
}
document.write(JSON.stringify(new_arr, null, 4))
var arr = [2, 4, 6];
var result = new Array(7);
arr.forEach(function(a) { result[a] = a;});
Try splice ():
var arr = [2, 4, 6];
var i = 0,
l = arr[arr.length - 1];
while (i < l) {
if(i !== arr[i])
arr.splice(i, 0, null);
i++;
}
console.log(arr); //[ null, null, 2, null, 4, null, 6 ]
Interesting poll:
var arr = [2, 4, 6]
var n = 0
while(arr.length > n) {
if(arr[n] !== n) {
arr = arr.slice(0,n).concat(null, arr.slice(n))
}
n++
}
console.log(arr) // [null, null, 2, null, 4, null, 6]
This approach is applied to an array consisting of a random number of sorted integers.
var arr = [2, 4, 6];
var narr = (new Array(arr.sort()[arr.length-1]))
arr.map(function(v){
narr[v] = v;
});
for (var i = 0; i<narr.length; i++) narr[i]||(narr[i]=null);
console.log(narr);