I don't know much about angular.js myself, but I can give some small tips about your code.

#Indentation

Code, in general, looks ugly without proper indentation.

I recommend that you indent the body of the second parameter passed into app.filter.

#Why are you checking with 'undefined'?

On the line that goes:

if (typeof categories != 'undefined') {

Why are you comparing with 'undefined'?

If you want to check is categories was defined, you could just do

if (categories) {

I don't know much about angular.js myself, but I can give some small tips about your code.

Indentation

Code, in general, looks ugly without proper indentation.

I recommend that you indent the body of the second parameter passed into app.filter.

Why are you checking with 'undefined'?

On the line that goes:

if (typeof categories != 'undefined') {

Why are you comparing with 'undefined'?

If you want to check is categories was defined, you could just do

if (categories) {