This is a bit of an unusual matrix, so I cannot find a nice way of constructing it with literals (not sure if it’s possible or not), but I would do this, which is pretty readable:
str = [["a", "b", "c"],
["d", "e", "f"],
["g", "h"],
["i", "j", "k", "lm"]]
num = [1, 2, 4, 9]
a = [str num]
As I said, this is a slightly odd matrix, are you sure that a matrix is the right data structure for what you are doing? Julia has a lot of nice data structures. If you are used to only using arrays, then it’s easy to overlook them.
Edit: Here’s a one-liner:
a = [[["a", "b", "c"], ["d", "e", "f"], ["g", "h"], ["i", "j", "k", "lm"]] [1, 2, 4, 9]]
Less readable, imho.