Q:

How to pick up keys only of type Array

I am using Angular JS with underscore JS
I have a JSON as shown above, from the above JSON, I am trying to pick up all the Keys which are of type array. 
[{
        "_id": "591c2748f6d215203ee12241",
        "LineSystemOid": "{00033457-0000-0000-F306-D0D1B64F1D04}",
        "LineName": "P-10148",
        "Filter1": [{
            "Reason_1": 1,
            "ReasonShrtStrngVal": "Working",
            "ReasonLngStrngVal": "Working"
        }],
        "Filter2": [{
            "Status_1": 1,
            "StatusShrtStrngVal": "Working",
            "StatusLngStrngVal": "Working"
        }],
        "DateCreated": "2012-05-18 22:54:18.637",
        "DateLastModified": "2014-05-15 22:43:27.533",
        "Filter3": [{
            "CorrelationStatus_1": null,
            "CorrelationStatusShrtStrngVal": null,
            "CorrelationStatusLngStrngVal": null
        }]

    }]

Means the output I need is Filter1, Filter2 and Filter3
I have tried as below, but the output I am getting is
var allkeys = _.keys(reasons[0]);
console.log(JSON.stringify(allkeys));

output:
["_id","LineSystemOid","LineName","Filter1","Filter2","DateCreated","DateLastModified"]

My Fiddle 
http://jsfiddle.net/vEDcx/10/

A:

My solution - http://jsfiddle.net/d226aco7/
var reasons =  [{
    "_id": "591c2748f6d215203ee12241",
    "LineSystemOid": "{00033457-0000-0000-F306-D0D1B64F1D04}",
    "LineName": "P-10148",
    "Filter1": [{
        "Reason_1": 1,
        "ReasonShrtStrngVal": "Working",
        "ReasonLngStrngVal": "Working"
    }],
    "Filter2": [{
        "Status_1": 1,
        "StatusShrtStrngVal": "Working",
        "StatusLngStrngVal": "Working"
    }],
    "DateCreated": "2012-05-18 22:54:18.637",
    "DateLastModified": "2014-05-15 22:43:27.533",
    "Filter2": [{
        "CorrelationStatus_1": null,
        "CorrelationStatusShrtStrngVal": null,
        "CorrelationStatusLngStrngVal": null
    }]

}]

var allkeys = [];
_.forEach(reasons[0], function(value, key) {
    if (_.isArray(value)) {
    allkeys.push(key);
  }
});

console.log(JSON.stringify(allkeys));

