Well, for starters you must note that you can't group in a matrix elements of different types. The boxing here helps because it puts all elements on the same foot: all boxes.
One thing you can do is format (":
) to text and stitch (,.
) instead of link (;
):
(~.y),. (2 ": "0 +/ "1 = y)
The 2 in 2 ":
serves as a format indicator, 2 digits-wide, padded with a blank space.
UPDATE:
Or in the style of Eelvex:
({. , 2&":&#) /. ~ y
There's a few elements that might be new here. Using append (,
) instead of stitch (,.
) because each result of key (/.
) is produced separately, we're not sticking two arrays side by side, but rather creating one big array one row at a time.