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<?php
//Block certain activity types from being added
function bp_activity_dont_save( $activity_object ) {
    $exclude = array(
        'updated_profile',
        'new_member',
        'new_avatar',
        'friendship_created',
        'joined_group'
    );

    // if the activity type is empty, it stops BuddyPress BP_Activity_Activity::save() function
    if( in_array( $activity_object->type, $exclude ) ) {
        $activity_object->type = false;    
    }
}

add_action('bp_activity_before_save', 'bp_activity_dont_save', 10, 1 );
?>