CODEWITHSUNDEEP
javascriptarraysloopssortingnumbers
idnamzciv
idnamzciv

Reputation: 23

Sorting an array with for loop failed

For fun, I started some JavaScript on CheckiO. With the median task I got a problem. First I tried to sort the given array with a for loop. To see the array during the loop I used a console.log.

for (var i = 0; i < data.length-1; i++) {
    if (data[i] > data[i+1]) {
        var temp = data[i];
        data[i] = data[i+1];
        data[i+1] = temp;
        i = 0;
    }
    console.log(data);
}

The problem is when there is only one number in the wrong position; the sorting stops and just prints out the array a few times. For example:

median([5,4,3,2,1])
[ 4, 5, 3, 2, 1 ]
[ 4, 3, 5, 2, 1 ]
[ 4, 3, 5, 2, 1 ]
[ 4, 3, 2, 5, 1 ]
[ 4, 2, 3, 5, 1 ]
[ 4, 2, 3, 5, 1 ]
[ 4, 2, 3, 5, 1 ]
[ 4, 2, 3, 1, 5 ]
[ 4, 2, 3, 1, 5 ]
[ 4, 2, 1, 3, 5 ]
[ 4, 1, 2, 3, 5 ]
[ 4, 1, 2, 3, 5 ]
[ 4, 1, 2, 3, 5 ]
[ 4, 1, 2, 3, 5 ]

Is there any explanation for this behavior? Thanks!

Upvotes: 2

Views: 173

Answers (4)

Daron Spaulding
Daron Spaulding

Reputation: 71

There is a great sort function implemented for you on JavaScripts Array prototype object.

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/sort

However, I'm betting you know this and are implementing this code for learning purposes.

The bug in your version relates to the incrementing of this variable i

Instead, try this:

var i = 0;
while(i < data.length) {
  if(data[i] > data[i + 1]) {
    var temp = data[i];
    data[i] = data[i + 1];
    data[i + 1] = temp;
    i = 0;
    continue;
  }

  i += 1;
}

Since we do not know the required number of iterations, it's more appropriate and clear to use a while loop instead of the for loop. This way, the code is clear and the incrementing of i is only done when the logical if statement evaluates to false.

Upvotes: 1

Kenneth Salomon
Kenneth Salomon

Reputation: 1390

The code you wrote looks fine except that it does not check for the first element due to the loop iteration adding +1 to the i value.

To fix this, just set your i = -1; instead of i = 0;.

median([5,4,3,2,1]);

function median(data) {
  for(var i = 0; i < data.length-1; i++) {
  		//console.log(i, data[i], data[i+1], data);
      if(data[i]>data[i+1]) {
          var temp = data[i];
          data[i] = data[i+1];
          data[i+1] = temp;
          i=-1; // Reset iterator so it is back to 0 on the next loop.
      }
      console.log(data);
  }
}

EDIT: I added a commented out line of code to the snippet. If you uncomment it and comment the other console.log, you will get outputs to the console that show you the index you're at, the value of that index, the value at the index you're comparing it to and then the current state of the array. Try changing the -1 to 0 and look at how it differs from having it reset to -1.

Upvotes: 0

Jarek Kulikowski
Jarek Kulikowski

Reputation: 1389

var a =[ 4, 5, 3, 2, 1 ];
var b =[ 4, 3, 5, 1, 2 ];
var c =[ 5, 3, 4, 2, 1 ];


function mySort(inArray) {
    return inArray.sort(function(x,y) { return x>y ? 1 : -1});
}

console.log( mySort(a) );
console.log( mySort(b) );
console.log( mySort(c) );

is this what you are looking for?

Upvotes: 0

Dij
Dij

Reputation: 9808

your code is failing because even though you make i=0 in if block, after iteration is finished i gets incremented and becomes 1, so it never checks for data[0] again. you can do something like this: 

var data = [5,4,3,2,1];

for(var i = 0; i < data.length;) {
  if(data[i]>data[i+1]) {
      var temp = data[i];
      data[i] = data[i+1];
      data[i+1] = temp;
      i = 0;
  }else{
      i++;
  }
  console.log(data);
}

Upvotes: 0

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