Output entry info for multiple channels in category loop

Question

How can I output the entry_ids for multiple channels within a category loop organized by channel?

I have 3 channels that share a category group so I need to loop through the categories and list out all entry ids but organized by their channel.

The info needs to be like so:

category 1 title
  - channel 1 (entry id 1, entry id 2, etc)
  - channel 2 (entry id 1, entry id 2, etc)
  - channel 3 (entry id 1, entry id 2, etc)

category 2 title
  - channel 1 (entry id 1, entry id 2, etc)
  - channel 2 (entry id 1, entry id 2, etc)
  - channel 3 (entry id 1, entry id 2, etc)

Hope that makes sense.

Any help is appreciated.

Answer 1

{exp:channel:categories}
   {category_name}
   {exp:channel:entries category="{category_id}" channel="channel1"}
      {if count == 1}{channel}{/if}
      {title}
   {/exp:channel:entries}
   {exp:channel:entries category="{category_id}" channel="channel2"}
      {if count == 1}{channel}{/if}
      {title}
   {/exp:channel:entries}
   {exp:channel:entries category="{category_id}" channel="channel3"}
      {if count == 1}{channel}{/if}
      {title}
   {/exp:channel:entries}
{/exp:channel:categories}

Beware performance issues if you have many categories and many entries!

Other ways just for the sake of it...

{exp:channel:categories}
   {category_name}
   {exp:channel:entries category="{category_id}" channel="channel1|channel2|channel3"}
      {channel}
      {title}
   {/exp:channel:entries}
{/exp:channel:categories}

Or reverse it:

{exp:channel:entries category="1|2|3" dynamic="no"}
    {categories}category_name{/categories}
    {channel}
    {title}
{/exp:channel:entries}