Django recipe: A django-tagging cloud for all models

By Ben Welsh • August 1, 2009

As far as I can tell, django-tagging will only create a cloud for one particular database model. This is usually awesome, but sometimes not enough. What if, for instance, you wanted to make a combined cloud that consolidated tags across more than one model? Maybe your blog puts tags not just on posts, but also on tweets and bookmarks.

That's pretty much the situation I was in, and here's how I hacked on the module's codebase to get it done. The code below accepts a queryset of TaggedItem objects and returns a list of tags and font sizes you can use to format the cloud, as I did here.

<div class="source"><pre>""" A modification of the tag cloud utilities in django-tagging. Necessary so I can run a tagcloud for all the models, not just one. Tip: It's good to submit a select_related query to avoid a ton of database hits. This will run a join that really slims things down. &gt;&gt;&gt; cloud.calculate_cloud(TaggedItem.objects.select_related().all()) """ import math from django.utils.translation import ugettext as _ # Font size distribution algorithms LOGARITHMIC, LINEAR = 1, 2 def _calculate_thresholds(min_weight, max_weight, steps): delta = (max_weight - min_weight) / float(steps) return [min_weight + i * delta for i in range(1, steps + 1)] def _calculate_tag_weight(weight, max_weight, distribution): """ Logarithmic tag weight calculation is based on code from the `Tag Cloud`_ plugin for Mephisto, by Sven Fuchs. .. _`Tag Cloud`: http://www.artweb-design.de/projects/mephisto-plugin-tag-cloud """ if distribution == LINEAR or max_weight == 1: return weight elif distribution == LOGARITHMIC: return math.log(weight) * max_weight / math.log(max_weight) raise ValueError(_('Invalid distribution algorithm specified: %s.') % distribution) def _group_tagged_items(tagged_item_qs): """ Accepts a queryset of TaggedItem objects, groups them by tag, and then counts their frequency. """ tag_count = {} for ti in tagged_item_qs: try: tag_count[ti.tag]['count'] += 1 except KeyError: tag_count[ti.tag] = {'font-size': None, 'count': 1} return tag_count def calculate_cloud(tagged_items_qs, steps=4, distribution=LOGARITHMIC, min_count=5): """ Add a ``font_size`` attribute to each tag according to the frequency of its use, as indicated by its ``count`` attribute. ``steps`` defines the range of font sizes - ``font_size`` will be an integer between 1 and ``steps`` (inclusive). ``distribution`` defines the type of font size distribution algorithm which will be used - logarithmic or linear. It must be one of ``tagging.utils.LOGARITHMIC`` or ``tagging.utils.LINEAR``. """ tag_counts = _group_tagged_items(tagged_items_qs) if len(tag_counts) &gt; 0: counts = [i['count'] for i in tag_counts.values()] min_weight = float(min(counts)) max_weight = float(max(counts)) thresholds = _calculate_thresholds(min_weight, max_weight, steps) for tag in tag_counts.keys(): font_set = False tag_weight = _calculate_tag_weight(tag_counts[tag]['count'], max_weight, distribution) for i in range(steps): if not font_set and tag_weight &lt;= thresholds[i]: tag_counts[tag]['font_size'] = i + 1 font_set = True # Cut off the data at the minimum count tag_list = [(k, v['font_size'], v['count']) for k,v in tag_counts.items() if v['count'] &gt; min_count] # Sort by count tag_list.sort(lambda x,y:cmp(x[2], y[2])) # Reverse that tag_list.reverse() return tag_list </pre></div>