Array filling in Javascript

Question

I need to fill 1 as an element of array FilteredRPeakThousandDataArray starting with index 500 in new array, and 0 for other index. Done like the following but the new array is getting filled only by 0. Explanation : at index 600,800,1200,1300 element in FilteredRPeakThousandDataArray should be 1 and 0 in all other indexes including for index 2(because 2 is less than 500)

var j = 500;
var FilteredRPeakDataArray = new Array();
var FilteredRPeakDataArray = [2, 600, 800, 1200, 1300];
var FilteredRPeakThousandDataArray = new Array();
for (var i = 0; i < 1500; i++) {
 if (FilteredRPeakDataArray[j] == i) {
 FilteredRPeakThousandDataArray[i] = 1;
 } else {
 FilteredRPeakThousandDataArray[i] = 0;
 }
 
 j++;
}
console.log("FilteredRPeakThousandDataArray " + FilteredRPeakThousandDataArray);

• Roy Bogado: you don't have the position 500 on FilteredRPeakDataArray, so, just compare j==i

Answer 1

You can simply use Array.from().

const FilteredRPeakDataArray = [2, 600, 800, 1200, 1300];
const FilteredRPeakThousandDataArray = Array.from({length: 1500},
 (_, i) => FilteredRPeakDataArray.includes(i) && i > 500 ? 1 : 0
);
console.log(FilteredRPeakThousandDataArray);

Answer 2

you had two problems

one is that you were advancing J index anyway

and the main one was this line : FilteredRPeakDataArray[j] == i

FilteredRPeakDataArray was an array with only 5 elements and you were going with huge indices. there is better ways to implement what you trying to do but I guess you are new to js (or maybe coding) so this fix will give you a better understanding of what went wrong

var startFrom = 500;
var j=0;
var FilteredRPeakDataArray = new Array();
var FilteredRPeakDataArray = [2,600,800,1200,1300];
var FilteredRPeakThousandDataArray = new Array();
 for (var i=0;i<1500;i++){
 if(FilteredRPeakDataArray[j]==i){
if( i > startFrom ){
 FilteredRPeakThousandDataArray[i] = 1;
}
 j++;
 }
 else{
 FilteredRPeakThousandDataArray[i] = 0;
 }
 }

Answer 3

You can create an array with 0 for all 1500 indexes using fill. Thne loop through FilteredRPeakDataArray and update only those indexes which have value> j

var j = 500;
var FilteredRPeakDataArray = [2, 600, 800, 1200, 1300];
var FilteredRPeakThousandDataArray = Array(1500).fill(0);
FilteredRPeakDataArray.forEach(n => {
 if(n > j)
 FilteredRPeakThousandDataArray[n] = 1;
})
console.log(FilteredRPeakThousandDataArray[2]);
console.log(FilteredRPeakThousandDataArray[600]);
console.log(FilteredRPeakThousandDataArray[800]);

• Code Maniac: it should be n >= j instead of n > j

Answer 4

const start = 500;
const limit = 1500;
const FilteredRPeakDataArray = [2, 600, 800, 1200, 1300];
// fill array with 1s
const FilteredRPeakThousandDataArray = new Array(limit).fill(1);
// change value of indices stored in FilteredRPeakDataArray to 0
for (const idx of FilteredRPeakDataArray) {
 if (idx >= start) {
 FilteredRPeakThousandDataArray[idx] = 0;
 }
}
console.log("FilteredRPeakThousandDataArray " + FilteredRPeakThousandDataArray);

Answer 5

I'd just pre-fill the array with 0 and then set 1 for those specific indexes:

var FilteredRPeakThousandDataArray = new Array(1500);
FilteredRPeakThousandDataArray.fill(0);
for (const index of FilteredRPeakDataArray) {
 if (index >= j) {
 FilteredRPeakThousandDataArray[index] = 1;
 }
}

Live Example:

var j = 500;
var FilteredRPeakDataArray = [2, 600, 800, 1200, 1300];
var FilteredRPeakThousandDataArray = new Array(1500);
FilteredRPeakThousandDataArray.fill(0);
for (const index of FilteredRPeakDataArray) {
 if (index >= j) {
 FilteredRPeakThousandDataArray[index] = 1;
 }
}
// Show results
for (const index of [0, ...FilteredRPeakDataArray]) {
 console.log(`FilteredRPeakThousandDataArray[${index}] = ${FilteredRPeakThousandDataArray[index]}`);
}

But if you want to set those values as you build the array, you can use Array.from's callback:

var FilteredRPeakThousandDataArray = Array.from({length: 1500}, (_, index) => {
 return index >= j && FilteredRPeakDataArray.includes(index) ? 1 : 0;
});

Live Example:

var j = 500;
var FilteredRPeakDataArray = [2, 600, 800, 1200, 1300];
var FilteredRPeakThousandDataArray = Array.from({length: 1500}, (_, index) => {
 return index >= j && FilteredRPeakDataArray.includes(index) ? 1 : 0;
});
// Show results
for (const index of [0, ...FilteredRPeakDataArray]) {
 console.log(`FilteredRPeakThousandDataArray[${index}] = ${FilteredRPeakThousandDataArray[index]}`);
}

---

Array#fill and Array.from are both relatively recent additions to JavaScript, but both can be polyfilled easily.

Answer 6

You can compare j with i and then check for particular value inside FilteredRPeakDataArray array

var j = 500;
var FilteredRPeakDataArray = new Array();
var FilteredRPeakDataArray = [2, 600, 800, 1200, 1300];
var FilteredRPeakThousandDataArray = new Array(1500).fill(0);
for (var i = 0; i < 1500; i++) {
 if (i >= j && FilteredRPeakDataArray.includes(i)) {
 FilteredRPeakThousandDataArray[i] = 1;
 } else {
 FilteredRPeakThousandDataArray[i] = 0;
 }
}
console.log( FilteredRPeakThousandDataArray);

Answer 7

You could fill the 1500 element array with 0's from the start, filter the array to those element greater than j, and replace all indices with 1's:

var j = 500;
var FilteredRPeakDataArray = [2, 600, 800, 1200, 1300];
var FilteredRPeakThousandDataArray = new Array(1500).fill(0);
FilteredRPeakDataArray.filter(el => el > j).map(el => FilteredRPeakThousandDataArray[el] = 1)
console.log("FilteredRPeakThousandDataArray " + FilteredRPeakThousandDataArray);

Answer 8

first fill all the elements of array with 0 's and later change the required indexes to 1

var j = 500;
var FilteredRPeakDataArray = new Array();
var FilteredRPeakDataArray = [2, 600, 800, 1200, 1300];
var FilteredRPeakThousandDataArray = new Array(1500).fill(0);
for (var i = 0; i < FilteredRPeakDataArray.length; i++) {
 
 FilteredRPeakDataArray[i]>=j ? FilteredRPeakThousandDataArray[FilteredRPeakDataArray[i]]=1:null
 
}
console.log("FilteredRPeakThousandDataArray " + FilteredRPeakThousandDataArray);