Format object with loadash and reduce, format by day, formay by month, groupby and sum by dates.

steps.js

/*    
  weekly = [
   ['3/6 - 3/12', 10],
   ['3/12 - 3/19', 13]
  ];
  day = [
   ['3/6', 10]
   ['3/8', 2]
  ];
  
  month = [
   ['jun', 10]
   ['feb', 2]
  ];
*/

// dateArray: [] of objects
// opt: String, 'day' or null to filter by month
function formatStepsBy(dateArray, opt) {
  
  var filter = opt === 'day' ? 'M/D' : 'MMM';

  return _.map(dateArray, function (item) {
    
    var date = moment(item.date).format(filter);
    return [date, item.steps];

  });
  
}

function sum(arr, key, val){
 
  return _.reduce(arr, function(result, item){
     
     result[item[key]] = result[item[key]] || 0;     
     result[item[key]] += item[val];
     
      return result;
  }, {});
}

_.mixin({
   sum: sum
});

function formatStepsWeekly(dateArray) {
    
  var groupDates = _.map(dateArray, function (item) {
     
    var groupBy = moment(item.date).startOf('isoweek').format('YYYY/MM/DD');
    item.groupBy = groupBy;
    
    return item;
  });
  
  var summed = _.sum(groupDates, 'groupBy', 'steps');
   
  return _.map(summed, function (item, key) {
    
    var start_date = moment(key).format('M/D');
    var end_date = moment(key).add(7, 'day').format('M/D');
     
    return [start_date +' '+ end_date, item];

  });
}

var stepsData = [
   {
     "date": "2016-03-01",
     "points": 394.4,
     "steps": 3650,
     "calories": 1687.4735,
     "activityCalories": 412.3124,
     "distance": 1.18
   },
   {
     "date": "2016-03-08",
     "points": 459.6,
     "steps": 4330,
     "calories": 1707.8484,
     "activityCalories": 412.3124,
     "distance": 1.3982
   },
   {
     "date": "2016-03-012",
     "points": 430.4,
     "steps": 4022,
     "calories": 1698.7234,
     "activityCalories": 412.3124,
     "distance": 1.2988
   },
   {
     "date": "2016-03-22",
     "points": 376,
     "steps": 3514,
     "calories": 1681.7235,
     "activityCalories": 412.3124,
     "distance": 1.1429
   }
];

console.log(formatStepsBy(stepsData, 'day'));
console.log(formatStepsBy(stepsData));
console.log(formatStepsWeekly(stepsData));