JS to find connected regions

findConnectedRegions.js

/* JS to find connected regions */

var findConnectedRegions = function(arr) {
  var distinct = []; 
  var durations = []; 
  var labels = []; 
  var idx = 0; 
  
  var calcCumSum = function(arr) {
    var calc = function(acc, n) {
        var lastNum = acc.length > 0 ? acc[acc.length-1] : 0;
        acc.push(lastNum + n);
        return acc;
    };
    return _.reduce(arr, calc, []);
  }

  for(i=0; i<arr.length; i++) { 
    if(_.indexOf(distinct, arr[i]) == -1) { 
      distinct.push(arr[i]); 
    }  

    if(_.isEmpty(durations) && _.isEmpty(labels)) { 
      durations.push(1); 
      labels.push(arr[i]);
      continue; 
    } 

    if(labels[idx] === arr[i]) {
      durations[idx] = durations[idx]+1;
    } else {
      labels.push(arr[i]);
      durations.push(1);
      idx++;
    }
  }

  return {
    durations: durations, 
    cumDurations: calcCumSum(durations),
    labels: labels, 
    distinct: distinct
  };

}