Javascript: grab object in array based on subobject value

Question

If I have this object:

DropIds = [
  {
    "studentId": 5,
    "dropboxItems": [
        {
            "dropBoxId": 230,
        }
    ]
  },
  {
    "studentId": 4,
    "dropboxItems": [
        {
            "dropBoxId": 585,
        },
        {
            "dropBoxId": 586,
        }
    ]
  }
]

And I try to run this code:

var result = $.grep(DropIds, function(e){
    return e.dropboxItems[0].dropBoxId == 585;
});

it will return a result, however if I change it from 585 to 586 the result is empty.

http://jsfiddle.net/tdb70f50/1/

So it looks like my code will only check the first object in the array.

How can I grab the object when there is more than one dropBoxId?

Thanks!

You need to also loop through the items of dropboxItems rather than just look at the first item. — Xotic750
– Xotic750, Commented Jan 16, 2015 at 22:42

Xotic750 · Accepted Answer · 2015-01-16 22:50:12Z

3

You need to check all the items in the array, not just the 0 index, you can use Array.prototype.filter

var result = DropIds.filter(function(item) {
    return item.dropboxItems.filter(function(box) {
        return box.dropBoxId == 586
    }).length
});

Demo: http://jsfiddle.net/56h7daod/

edited Jan 16, 2015 at 22:50

Xotic750

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answered Jan 16, 2015 at 22:45

tymeJV

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1 Comment

Andreas Over a year ago

You could replace the inner .filter() with .some() (and therefore remove the .length). This will only check box items until it finds the first match. fiddle

nanndoj · Accepted Answer · 2015-01-16 22:48:41Z

0

That's because you are only testing the first element (zero as index);

return e.dropboxItems[0].dropBoxId == 585;

you have to loop inside elements testing each object;

var result = $.grep(DropIds, function(e){
    if(!e.dropboxItems) return false;

    for(var i = 0; i < e.dropboxItems.length; i++) {
        if(e.dropboxItems[i].dropBoxId == 586) return true
    }

    return false;
});

http://jsfiddle.net/tdb70f50/2/

answered Jan 16, 2015 at 22:48

nanndoj

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Comments

JonnyReeves · Accepted Answer · 2015-01-16 22:54:26Z

0

In conjunction with the answers already provided, you can make good use of mapping and reducing to extract an array of nested dropBoxItems and then perform a search for a given dropBoxId, ie:

function getByDropBoxId(id, dropId) {
  return dropId
    // Pluck the nested arrays into a 2d array
    .map(function (dropId) {
      return dropId.dropboxItems;
    })
    // flatten / reduce them to a single array.
    .reduce(function (soFar, dropBoxItems) {
      return soFar.concat(dropBoxItems);
    }, [])
    // filter out the ones you are looking for and return the first.
    .filter(function(dropBoxItem) {
      return dropBoxItem.dropBoxId === id; 
    })[0];
};

answered Jan 16, 2015 at 22:54

JonnyReeves

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