Based on this answer on SO

:/^\s*-/,/^only/-1 !sort -u

provided the cursor is not placed anywhere on the lines starting with -

And, I don't know why

:/^\s*-/,/^\s*[^-]/-1 !sort -u

works only if cursor is positioned on the line immediately before start of search pattern

Based on this answer on SO

:/^\s*-/,/^only/-1 !sort -u

provided the cursor is not placed anywhere on the lines starting with -

And, I don't know why

:/^\s*-/,/^\s*[^-]/-1 !sort -u

works only if cursor is positioned on the line immediately before start of search pattern