JSFiddle - React, Tailwind, and code Playground

HTML

<script src="//cdnjs.cloudflare.com/ajax/libs/underscore.js/1.8.3/underscore-min.js"></script>

JavaScript

var bill  = [
  {
    "total": 5.21,
    "number": 3,
    "a": "Paid",
    "y": 2015,
    "m": 1,
    "d": "2015-01-17T23:58:34.115Z"
  },
  {
    "total": 374.65,
    "number": 3,
    "a": "Scheduled",
    "y": 2015,
    "m": 1,
    "d": "2015-01-18T02:16:03.503Z"
  },
  {
    "total": 310.84,
    "number": 1,
    "a": "Paid",
    "y": 2015,
    "m": 1,
    "d": "2015-01-17T23:58:34.115Z"
  },
  {
    "total": 284.41,
    "number": 3,
    "a": "Scheduled",
    "y": 2015,
    "m": 1,
    "d": "2015-01-18T02:16:03.503Z"
  }
]

var result = _.map(_.groupBy(data, 'a'), function(el, key) {
    return {
        key: key,
        values: _.map(el, function(item) {
            return [item.d, item.total];
        })
    };
});
console.dir(result);