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Message: [QUOTE="Uri Guttman, post: 4863071"] JE> There are four different cases you have to consider in your custom JE> compare function: JE> $h{$a} and $h{$b} exist ===> length($h{$a}) <=> length($h{$a}) JE> $h{$a} exists but $h{$b} doesn't ===> -1 JE> $h{$a} does't exist but $h{$b} does ===> 1 JE> Neither $h{$a} nor $h{$b} exists ===> 0 this is why doing a prefilter on the sort keys makes life much simpler. then you only have 1 real case to worry about - whether a key exists or not. you can replace a non-existant key with a fake one that always sorts higher than normal keys. this can be done in an ST or in the key extraction code in Sort::Maker. i leave how to do that as an exercise but it is much simpler than all the double sided checking you propose. uri [/QUOTE]