json-groupby.js

'use strict';
var propertyAt = require('./property-value.js')

function groupBy(items, properties, collect) {
  // TODO argument validation
  if (arguments.length < 2) return arr;
  var groups = _groupBy(items, properties);
  // collect other properties values in array
  if (collect && collect.length > 0)
    groups = collectProperties(groups, collect);

  return groups;
}

function _groupBy(items, properties) {
  var group = {};
 	if (typeof properties[0] === 'string') {
 	  group = groupByCategory(items, properties[0]);
 	} else {
 	  group = groupByRange(items, properties[0]);
 	}
  properties = properties.slice(1);
  if (properties.length > 0) {
    for (var key in group) {
      group[key] = _groupBy(group[key], properties);
    }
  }
  return group;
}

function groupByCategory(arr, prop) {
  return arr.reduce(function(group, item) {
    var tags = propertyAt(item, prop);
    tags.forEach(function(tag) { 
      group[tag] = group[tag] || [];
      group[tag].push(item);
    });
    return group;
  },{});
}

function groupByRange(arr, lookup) {
  return arr.reduce(function(group, f) {
    var val, ind, tag;
    val = propertyAt(f, lookup.property);
    ind = locationOf(val, lookup.intervals);
    if (ind === lookup.intervals.length -1) ind--;
    tag = lookup.labels ? lookup.labels[ind] : ind;
    group[tag] = group[tag] || [];
    group[tag].push(f);
    return group;
  },{});
}

// collect the properties in an array 
function collectProperties(groups, properties) { 
  var collection = {};
  for (var key in groups) {
    if (Array.isArray(groups[key])) {
      collection[key] = groups[key].reduce(function(coll, item) {
        properties.forEach(function(prop) { 
          if (!coll[prop]) coll[prop] = [];
          coll[prop] = coll[prop].concat(propertyAt(item,prop));
        })
        return coll;
      }, {})
    } else {
      collection[key] = collectProperties(groups[key], properties);
    }
  }
  return collection;
}

// similar to Array.findIndex but more efficient
// http://stackoverflow.com/q/1344500/713573
function locationOf(element, array, start, end) {
  start = start || 0;
  end = end || array.length;
  var pivot = parseInt(start + (end - start) / 2, 10);
  if (end-start <= 1 || array[pivot] === element) return pivot;
  if (array[pivot] < element) {
    return locationOf(element, array, pivot, end);
  } else {
    return locationOf(element, array, start, pivot);
  }
}
module.exports = groupBy;