Remove data from an array comparing it to an other array

Question

I am trying to compare the items in "item" array and the copyofOpList array to retrieve the data occurrences in copyofOpList

this is my try:

var _deleteUsedElement1 = function(item) {

                    for (var i = 0; i < item.length-1; i++){      
                          for (var j = 0; j< $scope.copyofOpList.length-1; j++){
                        if (item[i].operationCode == $scope.copyofOpList[j].code) {
                        $scope.copyofOpList.splice(j, 1);

                        } } } };

 $scope.compareArrays = function() {
     ...Get data from web Service
    _deleteUsedElement1(item);
  }

the copyofOpList array has 14 elements,and the item array has 2 array but my code deletes only one occurrence (the first),so please how can I correct my code,to retrieve any occurances in the copyofOpList array comparing to the item array thanks for help

tex · Accepted Answer · 2016-06-10 16:58:21Z

3

I'd try to avoid looping inside a loop - that's neither a very elegant nor a very efficient way to get the result you want.

Here's something more elegant and most likely more efficient:

var item = [1,2], copyofOpList = [1,2,3,4,5,6,7];

var _deleteUsedElement1 = function(item, copyofOpList) {
    return copyofOpList.filter(function(listItem) {
     return item.indexOf(listItem) === -1;
   });
  };

    copyofOpList = _deleteUsedElement1(item, copyofOpList);
    console.log(copyofOpList);
    //prints [3,4,5,6,7]
}

And since I just noticed that you're comparing object properties, here's a version that filters on matching object properties:

var item = [{opCode:1},{opCode:2}],
    copyofOpList = [{opCode:1},{opCode:2},{opCode:3},{opCode:4},{opCode:5},{opCode:6},{opCode:7}];

var _deleteUsedElement1 = function(item, copyofOpList) {
      var iOpCodes = item.map(function (i) {return i.opCode;});
      return copyofOpList.filter(function(listItem) {
        return iOpCodes.indexOf(listItem.opCode) === -1;
      });
    };

copyofOpList = _deleteUsedElement1(item, copyofOpList);
console.log(copyofOpList);
//prints [{opCode:3},{opCode:4},{opCode:5},{opCode:6},{opCode:7}]

Another benefit of doing it in this manner is that you avoid modifying your arrays while you're still operating on them, a positive effect that both JonSG and Furhan S. mentioned in their answers.

edited Jun 10, 2016 at 16:58

answered Jun 10, 2016 at 12:39

tex

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4 Comments

Furhan S. Over a year ago

Thats very elegant and concise. Though I would like to point out that its still looping inside a loop, because indexOf() is a loop in itself :)

JonSG Over a year ago

With your edits, this covers my answer so I will remove it.

tex Over a year ago

@FurhanS. Thanks, and you're right about the loop. I guess nested fors just hurt my eyes. There's also the question of whether the for is more or less efficient than the indexOf(). It seems that for was more efficient in the early days of indexOf(), but it also seems that the performance of indexOf() has improved and the situation may have even reversed in the interim (based on some quick googling, so don't hold me to it).

tex Over a year ago

@JonSG I thought your answer added to the discussion. I edited mine just now to mention the benefit of not altering the arrays while operating on them, which you also pointed out in your excellent answer.

Furhan S. · Accepted Answer · 2016-06-10 12:59:49Z

2

Splicing will change your array. Use a temporary buffer array for new values like this:

var _deleteUsedElement1 = function(item) {
    var _temp = [];
    for (var i = 0; i < $scope.copyofOpList.length-1; i++){      
        for (var j = 0; j< item.length-1; j++){
           if ($scope.copyofOpList[i].code != item[j].operationCode) {
               _temp.push($scope.copyofOpList[j]);
           } 
        } 
    } 
    $scope.copyofOpList = _temp;
};

edited Jun 10, 2016 at 12:59

answered Jun 10, 2016 at 12:28

Furhan S.

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3 Comments

tex Over a year ago

Have you tested this? I don't think it does what the requester needs.

Furhan S. Over a year ago

@Tex you were right. Didn't test the first time, hope the edited code does what is required as per my understanding. Thnx for pointing out.

JonSG Over a year ago

Hey, check out filter(), it kind of does what you are doing with _temp

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