2011/1/5 Florian Pflug <f...@phlo.org>: > 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).
Sorry, but It isn't too intuitive. Minimally for me. Why you don't thinking about simple functions with only positive arguments. There are only four combinations. I don't think we must have only one super function. we need functionality for: a) get first n items b) get items without last n items c) get last n items d) skip first n items I think so this functionality is relative important, so we can use a richer api. Maybe we thinking about different use cases. Pavel > > 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
