Split array into new array based on property occurences

Question

I have an array of objects that I would like to turn into an array (or array-like) object where the keys are the unique values for that given property (something like SQL group by).

fiddle:

var obj = [
   {
      "ClaimId":"111",
      "DrugName":"AMBIEN CR",
      "PatientId":1571457415
   },
   {
      "ClaimId":"222",
      "DrugName":"AMBIEN CR",
      "PatientId":1571457415
   },
   {
      "ClaimId":"333",
      "DrugName":"LOTREL",
      "PatientId":1571457415
   },
   {
      "ClaimId":"444",
      "DrugName":"METHYLPREDNISOLONE",
      "PatientId":1571457415
   },
   {
      "ClaimId":"555",
      "DrugName":"CYMBALTA",
      "PatientId":1513895252
   },
   {
      "ClaimId":"666",
      "DrugName":"CYMBALTA",
      "PatientId":1513895252
   },
   {
      "ClaimId":"777",
      "DrugName":"CYMBALTA",
      "PatientId":1513895252
   },
   {
      "ClaimId":"888",
      "DrugName":"CYMBALTA",
      "PatientId":1513895252
   },
   {
      "ClaimId":"147503879TMQ",
      "DrugName":"CYMBALTA",
      "PatientId":1513895252
   },
   {
      "ClaimId":"999",
      "DrugName":"CYMBALTA",
      "PatientId":1513895252
   }
]
function splitBy(data, prop) {
        var returnObj = {};
        var returnArray = [];
        $.each(data, function (ix, val) {
            if (returnObj[val[prop]] === undefined) {
                returnObj[val[prop]] = [];
                returnObj[val[prop]].push(val);
            }


        });
        console.log(returnObj);
    }
splitBy(obj,'PatientId');

In the fiddle you can see that I get the keys of the array like I want (the two unique values in the PatientId property) but I only get the first value. I understand that's because once the key is no longer undefined, then this check isn't ran, but I couldn't figure out quite how to do it and this is as close as I got. How can I do this with one iteration over this collection?

Bergi · Accepted Answer · 2014-03-24 20:35:55Z

4

I only get the first value.

That's because you only push the first value - when there had been no key. Change the

        if (returnObj[val[prop]] === undefined) {
            returnObj[val[prop]] = [];
            returnObj[val[prop]].push(val);
        }

to

        if (returnObj[val[prop]] === undefined) {
            returnObj[val[prop]] = [];
        }
        returnObj[val[prop]].push(val);

answered Mar 24, 2014 at 20:35

Bergi

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1 Comment

wootscootinboogie Over a year ago

After a few minutes of looking, this is exactly that I was trying to do with ternary logic if the val[prop] === something something..here, you simply push it onto the correct key because the correct key is what's being iterated over. Thanks :)

Travis J · Accepted Answer · 2014-03-24 20:59:23Z

1

jsFiddle Demo

You almost had it, but you forgot the else clause for once the key existed

if (returnObj[val[prop]] === undefined) {
    returnObj[val[prop]] = [];
    returnObj[val[prop]].push(val);
}else{
    returnObj[val[prop]].push(val);
}

edited Mar 24, 2014 at 20:59

answered Mar 24, 2014 at 20:36

Travis J

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7 Comments

Bergi Over a year ago

No, using else and an empty array literal would ignore the first occurence.

Evan Davis Over a year ago

With the else you have the same line twice; it shouldn't be in the if at all, because you want it to run every time.

wootscootinboogie Over a year ago

@Bergi I thought you were wrong at first, but...I was wrong when I realized that my new array was only 8 elements :(

Travis J Over a year ago

@Bergi - In your version it would. But not in the OP's code. Your comment is not relevant.

Travis J Over a year ago

@Mathletics - That is true, the else is not essentially required as much as the inclusion of the push, it is more of a readability issue. However, without refactoring the op's code, it is required.

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