How to GROUP and SUM json data using angular/ionic?

Question

I have a JSON object that looks like this:

  "Classes": [
    {
      "ID": "MATH101",
      "Class": "Math",
      "StudentCount": "2"
    },
    {
      "ID": "MATH101",
      "Class": "Math",
      "StudentCount": "8"
    },
    {
      "ID": "ENGLISH101",
      "Class": "English",
      "StudentCount": "13"
    }]

This JSON object is stored in $scope. How can I first group the data by Class and then SUM the StudentCount?

So the resulting JSON object would look something like this - ideally stored as a new scope variable:

  "Classes": [
    {
      "ID": "MATH101",
      "Class": "Math",
      "StudentCount": "10"
    },
    {
      "ID": "ENGLISH101",
      "Class": "English",
      "StudentCount": "13"
    }]

I've searched everywhere, and the only thing I can find are examples of doing this in conjunction with an ng-repeat, but I'm not using that here. I just need to massage this data for use in angular-chartjs.

Thank you very much for taking the time to look at my question.

Koushik Chatterjee · Accepted Answer · 2017-07-07 21:19:47Z

1

the transformation is just a logical part, your ng-repeat and all you can use then to render that in UI how you want.

here I am writing a function that will do the job for you

function populateSumArray(inputClasses) {
    opClasses = [];
    inputClasses.forEach(function(item) {
        var existing = opClasses.find(function(each) {
            return each.Class === item.Class;
        });
        if (existing) {
            existing.StudentCount = parseInt(existing.StudentCount) + parseInt(item.StudentCount);
        } else {
            opClasses.push(item);
        }
    });
    return opClasses;
}

and you can call this to transform it to a new array (calculated) and store it whereever you need. If you want to update the same scope variable then here is an example

$scope.Classes = populateSumArray($scope.Classes)

hope, it helps :)

answered Jul 7, 2017 at 21:19

Koushik Chatterjee

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6 Comments

NickyTheWrench Over a year ago

Thanks for your help! I'm getting inputClasses.forEach is not a function Any ideas?

Koushik Chatterjee Over a year ago

pass an array to the function, what exactly you are passing?

NickyTheWrench Over a year ago

I have the JSON object in a variable called $scope.classes. How do I pass this variable to your function so that it transforms the JSON?

Koushik Chatterjee Over a year ago

and your object $scope.classes have an property called Classes right? then try $scope.classes.Classes = populateSumArray($scope.classes.Classes)

NickyTheWrench Over a year ago

AHA! That did it! You're the man! But real quick - what if my StudentCount wasn't always an integer? What if it had decimals like 1.5? It looks like the parseInt is interfering with the decimals.

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