Group by within a Channel Entries loop

Question

I have banner ads stored in a channel and these are associated using a single entry Playa field with clients stored in another. I need to display random banners on a page but without ever showing more than one banner from each client.

Channel entries has no concept of 'Group By' so how am I best to go about doing this?

Update

In the end I wrote an extension to do this though the answer below would work equally well. You can download the 'Group By' extension here - https://github.com/ninefour/group_by.ext.ee_addon

Answer 1

I would use Stash to do this. See the example on the Stash wiki about grouping by with categories, which should work similar for the Playa field you have.

Within a banner's loop first create a stash list (by appending) of the banner ads with the client's id in name, something like

{exp:stash:append_list name="banner_{*playa field client entry id tag*}"}

then within a client's loop output the stash list, limiting the amount of banners to 1, like

{exp:stash:get_list name="banner_{*playa field client entry id tag*}" limit="1"}