example-usage.js

module.exports.beforeRender = function(elem, data) {
  console.log("Hi there, before render!");
  data.Grouped = groupBy(
    data.Sheet1,
    function(item) {
      return item.Course;
    },
    function(group) {
      return {};
    },
    function(a, b) {
      if (a.Name < b.Name) {
        return -1;
      } else if (b.Name < a.Name) {
        return 1;
      } else {
        return 0;
      }
    },
    function(a, b) {
      if (a.Special < b.Special) {
        return -1;
      } else if (b.Special < a.Special) {
        return 1;
      } else {
        return 0;
      }
    }
  );
  
}

group-by.js

/*
 * list: A list of Javascript objects
 * groupNameFn: A function that takes an item from the list and returns the name of the group
 * groupDetailsFn: A function that is provided the items of the group and returns an object of details about the gorup, to be added to the group element
 * groupSortFn: A Javascript function that sorts the groups, adorned with the details, and containing the name: property 
 * itemSortFn: A Javascript function that sorts items in the group
 *
 * Returns:
 * An ordered list of groups. Each group is an object wtih properties name and items.  
 * Items is the list of members in that group.
 * 
 * [
 * ]
 */
function groupBy(list, groupNameFn, groupDetailsFn, groupSortFn, itemSortFn) {
  var groups = {};
  
  // Generate group names
  for (var i = 0; i < list.length; i++) {
    var groupName = groupNameFn(list[i]);
    if (typeof groups[groupName] == 'undefined') {
      groups[groupName] = {
        name: groupName,
        items: [list[i]]
      }
    } else {
      groups[groupName].items.push(list[i])
    }
  }
  
  // Now form the result variable
  var ret = [];
  for (var name in groups) {
    ret.push(groups[name]);    
  }
  
  // Add details about each group
    if (groupDetailsFn) {
    for (var i = 0; i < ret.length; i++) {
      var details = groupDetailsFn(ret[i]);
      for (var key in details) {
        ret[i][key] = details[key];
      }
    }
  }

  // sort the groups
  if (groupSortFn) {
    ret.sort(groupSortFn);
  }

  // sort the items in each group
  if (itemSortFn) {
    for (var i = 0; i < ret.length; i++) {
      ret[i].items.sort(itemSortFn)
    }
  }
  return ret;
}