AngularJS Group By Directive without External Dependencies

Question

I\'m new to Angular and would like to learn the best way to handle a problem. My goal is to have a reusable means to create group by headers. I created a solution which wor

Answer 1

The code by JoshMB will not work correctly of you have multiple filters on the same dataset in the same view. The second time you group a filtered version of the dataset, it will change the same attribute in the original object, thus breaking the group breaks in the previously filtered versions.

I solved this by adding the name of the "CHANGED" attribute as en extra filter parameter. Below is my updated version of the code.

/*
 * groupBy
 *
 * Define when a group break occurs in a list of items
 *
 * @param {array}  the list of items
 * @param {String} then name of the field in the item from the list to group by
 * @param {String} then name boolean attribute that indicated the group changed for this filtered version of the set

 * @returns {array} the list of items with an added field name named with "_new"
 *                  appended to the group by field name
 *
 * @example     

 *              
{{item.groupfield}}
 *              
 *              

 *              
{{item.groupfield}}
 *
 *              Typically you'll want to include Angular's orderBy filter first
 */

app.filter('groupBy', ['$parse', function ($parse) {
    return function (list, group_by, group_changed_attr) {

        var filtered = [];
        var prev_item = null;
        var group_changed = false;
        // this is a new field which is added to each item where we append "_CHANGED"
        // to indicate a field change in the list
        //var new_field = group_by + '_CHANGED'; //- JB 12/17/2013
        var new_field = 'group_by_CHANGED';
        if(group_changed_attr != undefined) new_field = group_changed_attr;  // we need this of we want to group different filtered versions of the same set of objects !

        // loop through each item in the list
        angular.forEach(list, function (item) {

            group_changed = false;

            // if not the first item
            if (prev_item !== null) {

                // check if any of the group by field changed

                //force group_by into Array
                group_by = angular.isArray(group_by) ? group_by : [group_by];

                //check each group by parameter
                for (var i = 0, len = group_by.length; i < len; i++) {
                    if ($parse(group_by[i])(prev_item) !== $parse(group_by[i])(item)) {
                        group_changed = true;
                    }
                }


            }// otherwise we have the first item in the list which is new
            else {
                group_changed = true;
            }

            // if the group changed, then add a new field to the item
            // to indicate this
            if (group_changed) {
                item[new_field] = true;
            } else {
                item[new_field] = false;
            }

            filtered.push(item);
            prev_item = item;

        });

        return filtered;
    };
}]);