I want to make a list of dominoes. My attempt is as follows.
Subsets[#, {2}]~Join~Thread[{#, #}] &@Range[0, 6]
{{0,1},{0,2},{0,3},{0,4},{0,5},{0,6},{1,2},{1,3},{1,4},{1,5},{1,6},{2,3},{2,4},{2,5},{2,6},{3,4},{3,5},{3,6},{4,5},{4,6},{5,6},{0,0},{1,1},{2,2},{3,3},{4,4},{5,5},{6,6}}
Is there any simpler way to generate dominoes?