Gradebook

Further to my above post I've found out a few things.

1) Grader preferences are per-user and stored in mdl_user_preferences.grade_report_grader_collapsed_categories.

2) The data is serialised so it could look something like this:

a:2:{s:14:"aggregatesonly";a:5:{i:0;s:3:"613";i:1;s:3:"614";i:2;s:3:"615";i:3;s:3:"616";i:4;s:3:"617";}s:10:"gradesonly";a:0:{}}

...which makes my brain hurt! I want to be able to manipulate this code directly, to 'bulk' collapse a gradebook's categories. Is there someone who has had experience of this who can point me in the right direction? I don't want to reinvent the wheel.

-P.