knockout arraygetdistinctvalues of objects

问题:

I want to use ko.utils.arrayGetDistinctValues like in this fiddle on more than one property in an array so I map the array to an array of just the two properties I want

viewModel.justCategories = ko.dependentObservable(function() {
    var categories = ko.utils.arrayMap(this.items(), function(item) {
        return { catid : item.catid(), category : item.category() };
    });
    return categories.sort();
}, viewModel);

then I try to use arrayGetDistinctValues but it doesn't seem to work on objects.

viewModel.uniqueCategories = ko.dependentObservable(function() {
    return ko.utils.arrayGetDistinctValues(viewModel.justCategories()).sort();
}, viewModel);

My modified fiddle here

Can someone tell me how to do this?

回答1:

arrayGetDistinctValues only works with primitive values. For objects, you'll need a different approach. Here's a version that works.

viewModel.uniqueCategories = ko.dependentObservable(function() {
    var seen = [];
    return viewModel.justCategories().filter(function(n) {
        return seen.indexOf(n.catid) == -1 && seen.push(n.catid);
    });
});

http://jsfiddle.net/mbest/dDA4M/2/

回答2:

As an update to Michael Best's answer, here is something using more recent KnockoutJS v3 code conventions (e.g. dependentObservable = computed and using arrayFilter method):

var uniqueSizes = ko.computed({read: function() {
    var seen = [];
    return ko.utils.arrayFilter(viewModel.collection.vendorGearFilters(), function(f) {
        return seen.indexOf(f['size_abbr']()) == -1 && seen.push(f['size_abbr']());
    });
}, deferEvaluation: true})