Hi 4331 is IOS-XE that supports flexible netflow but the 3845 is IOS thats the older standard way and also random sample netflow using flow-sampler-map
http://www.cisco.com/c/en/us/td/docs/ios/12_0s/feature/guide/nfstatsa.html
http://www.cisco.com/c/en/us/td/docs/ios-xml/ios/fnetflow/configuration/xe-3s/fnf-xe-3s-book/fnf-fnetflow.html#d4759e8658a1635