How best to create and use associative array type in Postgres?

[Shaozhong SHI <shishaozhong@xxxxxxxxx>]

In Oracle, one can create and use associative array.  For instance,

TYPE FID_MEASURE IS TABLE OF NUMBER INDEX BY VARCHAR2(38);

NODES_WAITING FID_SET;

How best to create and use associative array type in Postgres?

Or, what is the best/most efficient equivalent in Postgres?

Regards,

David