Table lookup in Postgresql

Hi All

I have a table that contains arrays of integers. These integers
are code names for quantities. Each quantity (hence integer) has also
an associated index in a bigger array.

For example

Row in Table A
{5,6,7,8,9}

Table B contains the look up for the indices

Val Idx
5 10
6 1
7 9
8 2
9 3

What I would like to do is to create a row in table C for all rows in table
A that contains a vector where the indices corresponding to the elements in
the A table are 1 and the remainder are 0 like

{ 0,1, 1,0,0,1,0,0,1,1}

where the maximum length of this vector is known

How can I best do it in Postgresql? Should I loop using PL/PgSQL?

Thanks
Mehmet