Create monthly mean by time intervals
问题 Sorry if this has already been posted but I looked really hard and could not find anything. I am working with monthly temperature observations for 30 years, comprising January 1960 to December 1989. It looks like this: > head(df) date temp 1 1960-01-01 22.92235 2 1960-02-01 23.07059 3 1960-03-01 23.10941 4 1960-04-01 20.78353 5 1960-05-01 17.45176 6 1960-06-01 17.31765 First, what I need to do is to average all januaries, februaries, marches and etc for the whole period. Then, I would like to