Re: proposal: support empty string as separator for string_to_array

On Mon, Jul 27, 2009 at 12:42 PM, Pavel Stehule<pavel(dot)stehule(at)gmail(dot)com> wrote:
> 2009/7/25 Merlin Moncure <mmoncure(at)gmail(dot)com>:
>> On Fri, Jul 24, 2009 at 11:40 PM, Pavel Stehule<pavel(dot)stehule(at)gmail(dot)com> wrote:
>>> Hello
>>>
>>> I have one idea, that should simplify string to char array
>>> transformation. The base is idea: between every char is empty string,
>>> so empty string is regular separator for string_to_array function.
>>> This behave is inversion of array_to_string function behave:
>>>
>>> postgres=# select array_to_string(array['a','b','c'],'');
>>>  array_to_string
>>> -----------------
>>>  abc
>>> (1 row)
>>>
>>> postgres=# select string_to_array('abc','');
>>>  string_to_array
>>> -----------------
>>>  {a,b,c}
>>> (1 row)
>>
>> postgres=# select regexp_split_to_array('abc', '');
>>  regexp_split_to_array
>> -----------------------
>>  {a,b,c}
>> (1 row)
>>
>> :-)
>>
>
> I tested  implementation and it's about 30% faster than using regexp.
>
> I could to thing, 30% is significant reason for implementation.

yes, I noticed that too. I was thinking though that if anything
should be done, it should be to go the other way: simple cases of
regexp_split_to_array should use the simpler algorithm in
'string_to_array'...just not the '' case, since they produce different
results.

I don't think the chars_to_array function is the way to go. One thing
that might work though is to overload the string_to_array function (or
use default parameter) to control the empty string case with an bool,
or an option or something.

merlin