On Jan5, 2011, at 13:08 , Pavel Stehule wrote: > 2011/1/5 Florian Pflug <f...@phlo.org>: >> On Jan5, 2011, at 10:25 , Peter Eisentraut wrote: >>> On sön, 2011-01-02 at 12:47 +0100, Florian Pflug wrote: >>>> The only way around that would be to introduce magic constants "lower", >>>> "upper" that >>>> can be used within index expressions and evaluate to the indexed >>>> dimension's lower >>>> and upper bound. You'd then use >>>> >>>> my_array[upper], my_array[upper-1], ... >>>> >>>> to refer to the last, second-to-last, ... element in the array. Actually >>>> doing this >>>> could get pretty messy, though - not sure if it's really worth the >>>> effort... >>> >>> How about just some functions: >>> >>> array_first(array, dim) >>> array_last(array, dim) >> >> >> You image these to return the actual element, not the first and last index >> value, right? >> Because we already have array_lower() and array_upper() which return the >> lower and upper >> index bound for a certain dimension. >> (http://www.postgresql.org/docs/9.0/interactive/functions-array.htm) >> >> A more general solution would be a function >> >> array_relative(array anyarray, indices int[]) >> > > I don't think so this design helps. instead maintaining a data array, > you should to maintain a indices array.
How so? You'd still be able to get the last element by simply writing array_relative(some_array, array[-1]). Or, if we made the function variadic, by writing array_relative(some_array, -1). It's essentially what the OP proposed, but with the function array_relative() in place of the indexing operator []. best regards, Florian Pflug -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
