How to change group permissions in sharepoint 2013 using C#

Question

I have a group "Visitors" with Contribute permission and I want to change permission to Read, programmatically. I don't have problem with adding new permission to the group, but I don't know how to remove old permission.

How to change this code to remove permission Contribute and add permission Read?

SPWeb root = site.RootWeb;
SPGroup group = root.SiteGroups["Visitors"];  
SPRoleDefinition roleDefinition = root.RoleDefinitions.GetByType(SPRoleType.Reader);
SPRoleAssignment roleAssignment = new SPRoleAssignment(group);
roleAssignment.RoleDefinitionBindings.Add(roleDefinition);
root.RoleAssignments.Add(roleAssignment);
root.Update();

Answer 1

The following example demonstrates how to:

• add Reader permission Level to the group
• remove Contribute permission Level from the group

Example:

SPWeb root = site.RootWeb;
SPGroup group = root.SiteGroups[groupName];

SPRoleDefinition contributeRoleDef = root.RoleDefinitions.GetByType(SPRoleType.Contributor);
SPRoleDefinition readerRoleDef = root.RoleDefinitions.GetByType(SPRoleType.Reader);
SPRoleAssignment groupRoleAssignments = root.RoleAssignments.GetAssignmentByPrincipal(group);
groupRoleAssignments.RoleDefinitionBindings.Remove(contributeRoleDef);
groupRoleAssignments.RoleDefinitionBindings.Add(readerRoleDef);
groupRoleAssignments.Update();