Grouping and summarizing To date you have been answering questions about unique state-12 months pairs, but we may be interested in aggregations of the information, like the common existence expectancy of all countries inside of annually. Higher education homework and my assignments always managed to acquire me worked up. http://elliotrhsky.dsiblogger.com/14972800/the-single-best-strategy-to-use-for-r-programming-homework-help