library(dplyr)
library(lubridate)
df <- data.frame(date = seq(as.Date('2020-01-01'), as.Date('2020-12-31'), by = 'day'),
sales = rnorm(366, mean = 100, sd = 20))
df <- df %>%
mutate(month = month(date))
df_summary <- df %>%
group_by(month) %>%
summarise(avg_sales = mean(sales))
df_summary
输出结果将是一个包含月份和平均销售值的表格。