Re: proposal: searching in array function - array_position

Hi

I am sending updated version - it allow third optional argument that
specify where searching should to start. With it is possible repeatably
call this function.

Regards

Pavel

2015-01-17 23:43 GMT+01:00 Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>:

> Hi
>
> here is a proof concept of array_offset function
>
> possible question:
>
> * used comparation "=" or "IS NOT DISTINCT FROM"
>
> In this initial proof concept I used "IS NOT DISTINCT FROM" operator - but
> my opinion is not strong in this question. Both has some advantages and
> disadvantages.
>
> Regards
>
> Pavel
>
>
> 2015-01-16 19:12 GMT+01:00 Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>:
>
>>
>>
>> 2015-01-16 18:37 GMT+01:00 Jim Nasby <Jim(dot)Nasby(at)bluetreble(dot)com>:
>>
>>> On 1/16/15 11:16 AM, Pavel Stehule wrote:
>>>
>>>>
>>>>
>>>> 2015-01-16 17:57 GMT+01:00 Jim Nasby <Jim(dot)Nasby(at)bluetreble(dot)com <mailto:
>>>> Jim(dot)Nasby(at)bluetreble(dot)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
>>>
>>
>>
>