need substring based on delimiter

Hi:

I want to create a string from the first 3 elements of a csv (for example). The csv is longer than 3 elements. Example...

aaa,bbb,ccc,ddd,eee,fff,ggg

I want the string "aaa,bbb,ccc".

Tried splitting this to an array (precursor to appending elements 1,2,3), but failed to be able to reference the elements returned...

stdb_a0=# select string_to_array('aaa,bbb,ccc,ddd,eee,fff,ggg',',');
string_to_array
-------------------------------
{aaa,bbb,ccc,ddd,eee,fff,ggg}
(1 row)

stdb_a0=# select string_to_array('aaa,bbb,ccc,ddd,eee,fff,ggg',',')[1];
ERROR: syntax error at or near "["

If there was a way "position" would return the pos of the 3rd comma, I could use sustring. But I don't think it can :-(