Create arrays from 1D array after every nth occurrence using Angular JS - angularjs

Question

I have an array which looks like this
Array[20]
0 : "2"
1 : "3"
2 : "4"
3 : "5"
4 : "6"
5 : "7"
6 : "8"
7 : "9"
8 : "10"
9 : "11"
10: "12"
11: "13"
12: "14"
13: "15"
14: "16"
15: "17"
16: "18"
17: "19"
18: "20"
19: "12"
Now I want to create arrays after every 4th occurrence like this
First Array
0 : "2"
1 : "6"
2 : "10"
3 : "14"
4 : "18"
Second Array
0 : "3"
1 : "7"
2 : "11"
3 : "15"
4 : "19"
and so on...
Yet I have written this code
for (var i = 0; i < $scope.data.effort.length; i = i+ 4) {
efforts.push( $scope.data.effort[i]);
};
From above code I am getting only first array what should I need to do to get remaining arrays. Please help

Answer 1

All you need is to run an extra loop outside that which handles your starting index. LIke this:
efforts = []
for (var j = 0; j < arr.length / 4; j++) {
efforts[j] = []
for (var i = j; i < arr.length; i = i + 4) {
efforts[j].push(arr[i]);
};
console.log(efforts[j])
}
Here's working example: (simplified in JS, without $scope and all)
var arr = [
"2", "3", "4", "5", "6", "7", "8", "9", "10", "11", "12", "13", "14",
"15", "16", "17", "18", "19", "20", "12"
]
efforts = []
for (var j = 0; j < arr.length / 4; j++) {
efforts[j] = []
for (var i = j; i < arr.length; i = i + 4) {
efforts[j].push(arr[i]);
};
console.log(efforts[j])
}
Or, interestingly, you can use the beast, I mean, reduce to achieve the same. :)
var arr = [
"2", "3", "4", "5", "6", "7", "8", "9", "10", "11", "12", "13", "14",
"15", "16", "17", "18", "19", "20", "12"
]
efforts = arr.reduce(function(arr, cur, curIndex) {
arr[curIndex % 4] = arr[curIndex % 4] || [];
arr[curIndex % 4].push(cur);
return arr
}, [])
console.log(efforts)

Answer 2

Another simple way with array filter:
var originalArray =["2","3","4","5","6","7","8","9","10","11","12","13","14","15","16","17","18","19","20","21"];
var firstArray = originalArray.filter((el, index) => (index%4 === 0));
var secondArray = originalArray.filter((el, index) => (index%4 === 1));
and so on