SAN FRANCISCO (AP) — Twitter says it has bought its data partner Gnip, which provides analysis of the more than 500 million tweets its users share each day — to advertisers, academic institutions, politicians and other customers. Twitter Inc. said Tuesday that Gnip has already played a “crucial role” in collecting and digesting the public data that people share on its short messaging service. Twitter says it plans to offer more sophisticated data analysis with the help of Gnip.