JavaScript Function Insertion Sorting/ Function undefined

Question

I am attempting to write a javascript file that has a insertion sort function, a function to check a sorted array and return true or false, and an insertion sort function that works from the end of the array index to the beginning. Here is the code i have

function insertionSort(arr) { 
    for(var i = 1; i < arr.length; i++) { 
        var val = arr[i]; var j; for(j = i; j > 0 && arr[j-1] > val; j--) {
            arr[j] = arr[j-1]; } arr[j] = val; }
    }
function reverseInsertionSort(arr) { 
    for(var i = arr.length; i >1; i--) 
    { var val = arr[i]; var j;
        for(j = i; j > 0 && arr[j-1] > val; j--)
            { arr[j] = arr[j-1]; } arr[j] = val;
            } }
var length = Math.floor(Math.random()*100)+1;
var arr = new Array();
for(let i = 0; i < length; i++) {
  arr.push(Math.floor(Math.random()*10000)+1);
}
console.log(arr);
//function sortCheck(arr) {
//for( var i = 0 ; i < arr.length; i++){
//  if(arr[i]>rr[i+1]){
//      return false
//  }
//}
//return true}


var sortedArr = insertionSort(arr);
console.log(sortedArr);
console.log("And with reverse \n");
var reverseSortedArr = reverseInsertionSort(arr);
console.log(reverseSortedArr);
//console.log(sortCheck(sortedArr));

The issue I am having right now is that sortedArr is undefined when output with console.log, it appears that the issue is that my function is "undefined" but seeing how i define it above, i dont understand how that is.

The formatting in this code makes my brain hurt. Why do you have multiple statements piled up in a single line? — JLRishe
– JLRishe, Commented Feb 7, 2019 at 3:27

Our_Benefactors · Accepted Answer · 2019-02-07 03:10:59Z

2

Your insertionSort function doesn't return a value, it modifies the array passed as an argument. Instead of var sortedArr = insertionSort(arr), just call insertionSort(arr) and then do console.log(arr).

answered Feb 7, 2019 at 3:10

Our_Benefactors

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1 Comment

William Machado Over a year ago

thank you! its been a while since i've used javascript

ellipsis · Accepted Answer · 2019-02-07 03:11:53Z

0

You have to return arr from the function. It is not returning anything that's why you are getting undefined

function insertionSort(arr) { 
    for(var i = 1; i < arr.length; i++) { 
        var val = arr[i]; var j; for(j = i; j > 0 && arr[j-1] > val; j--) {
            arr[j] = arr[j-1]; } arr[j] = val; }
   return arr; }
function reverseInsertionSort(arr) { 
    for(var i = arr.length; i >1; i--) 
    { var val = arr[i]; var j;
        for(j = i; j > 0 && arr[j-1] > val; j--)
            { arr[j] = arr[j-1]; } arr[j] = val;
            } return arr}
var length = Math.floor(Math.random()*100)+1;
var arr = new Array();
for(let i = 0; i < length; i++) {
  arr.push(Math.floor(Math.random()*10000)+1);
}
console.log(arr);



var sortedArr = insertionSort(arr);
console.log(sortedArr);
console.log("And with reverse \n");
var reverseSortedArr = reverseInsertionSort(arr);
console.log(reverseSortedArr);
//console.log(sortCheck(sortedArr));

answered Feb 7, 2019 at 3:11

ellipsis

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2 Comments

Our_Benefactors Over a year ago

It's considered a bad practice to modify an array and return it. You should either return a new array without modifying the argument, or modify the argument. Not both - this can cause nasty side effects.

Patrick Roberts Over a year ago

@Our_Benefactors Array.prototype.sort(), and Array.prototype.reverse() would suggest otherwise. That's nonsense. Document behavior and return the reference if you want, it's useful for chaining and other common language patterns.

Josh Wood · Accepted Answer · 2019-02-07 03:16:38Z

0

Make sure you return the array from the function(s). Since you currently are not, assigning the function to a variable would not yield any particular value.

function insertionSort(arr) { 
    for(var i = 1; i < arr.length; i++) { 
        var val = arr[i]; 
        var j; 
        for(j = i; j > 0 && arr[j-1] > val; j--) {
            arr[j] = arr[j-1]; 
        } 
        arr[j] = val; 
     } 
    return arr
}

answered Feb 7, 2019 at 3:16

Josh Wood

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