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Mathematica, 20 bytes
PadRight@Range@#&
Contains U+F3C7 (Mathematica's builtin Transpose function)
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Usage
PadRight@Range@#&[{3, 5, 2, 1, 6}]
{{1, 1, 1, 1, 1}, {2, 2, 2, 0, 2}, {3, 3, 0, 0, 3}, {0, 4, 0, 0, 4}, {0, 5, 0, 0, 5}, {0, 0, 0, 0, 6}}
Explanation
P...