Converting to number with given format

Hello,
I'd like to convert a string number to a number being able to provide the
custom format.
With dates it works perfectly fine, so that I can do:

SELECT to_date('18 09 10', 'YY MM DD')

Is there something similar with numbers?

SELECT to_number('9,000', some_format) = 9;
SELECT to_number('9,000', another_format) = 9000;

It is not clear to me what some_format should be and what another_format
should be so that those selects are equal.

I've read the documentation but I can't find a similar example. In
stackoverflow they don't provide a solution either:
https://stackoverflow.com/questions/18882942/postgresql-convert-a-string-with-commas-into-an-integer

Thanks
Gabriel Fürstenheim