Your solution fails to sort by the alpha prefix first. See dragonchild's answer, above, which groups files first by their alpha prefix, then numerically by suffix.

Update: jdporter's solution (here) might be even more efficient with this dataset, since it uses \D+ (non-digits) rather than \w+ (word characters) to match the prefix, but it will also match punctuation and other non-alpha characters (which may not be what you want).