an anyone explain me what I'm doing wrong here :

[code]

dstring[][dstring] providor_symbol_map;

...

writeln(providor_symbol_map.keys.sort!((x,y)=>providor_symbol_map[x].length>=providor_symbol_map[y].length));

[/code]

output:

core.exception.RangeError@std.algorithm(9429): Range violation