I am proposing a simple function, that returns a position of element in array.
Yes please!
FUNCTION array_position(anyarray, anyelement) RETURNS int
That won't work on a multi-dimensional array. Ideally it needs to accept a slice or an element and return the specifier for the slice.
It is question, what is a result - probably, there can be a multidimensional variant, where result will be a array
array_position([1,2,3],2) --> 2 array_position([[1,2],[2,3],[3,4]], [2,3]) --> 2 /* 2nd parameter should to have N-1 dimension of first parameter */
The problem with that is you can't actually use '2' to get [2,3] back:
select (array[[1,2,3],[4,5,6],[7,8,9]])[1] IS NULL; ?column? ---------- t (1 row)
yes, but when you are searching a array in array you can use a full slice selection:
postgres=# select (ARRAY[[1,2],[4,5]])[1][1:2]; -- [1:2] should be a constant every time in this case -- so it should not be returned array --------- {{1,2}} (1 row)
I think the bigger problem here is we need something better than slices for handling subsets of arrays. Even if the function returned [2:2] it's still going to behave differently than it will in the non-array case because you won't be getting the expected number of dimensions back. :(
you cannot to return a slice and I don't propose it, although we can return a range type or array of range type - but still we cannot to use range for a arrays.
another question is how to solve more than one occurrence on one value - probably two sets of functions - first returns first occurrence of value, second returns set of occurrence
Gee, if only way had some way to return multiple elements of something... ;P
In other words, I think all of these should actually return an array of positions. I think it's OK for someone that only cares about the first instance to just do [1].
there can be two functions - "position" - returns first and "positions" returns all as a array
-- Jim Nasby, Data Architect, Blue Treble Consulting Data in Trouble? Get it in Treble! http://BlueTreble.com