2015-01-16 18:37 GMT+01:00 Jim Nasby <jim.na...@bluetreble.com>: > On 1/16/15 11:16 AM, Pavel Stehule wrote: > >> >> >> 2015-01-16 17:57 GMT+01:00 Jim Nasby <jim.na...@bluetreble.com <mailto: >> jim.na...@bluetreble.com>>: >> >> On 1/16/15 3:39 AM, Pavel Stehule wrote: >> >> 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. > > array_position_md([1,2,3],2) --> [2] >> array_position_md([[1,2],[2,3],[3,4]], 2) --> [2,1] >> >> 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 >