如何在R语言中高效生成按星期、小时排序的全周时段列表？

方法1：使用outer函数（最简洁高效） #

outer函数可以直接生成两个向量的所有元素组合，配合paste完成拼接，最后转成向量即可得到预期顺序的结果：

weekdays <- c("Mon","Tue","Wed","Thu","Fri","Sat","Sun")
hours <- c("12am","1am","2am","3am","4am", "5am","6am","7am","8am","9am","10am",
           "11am","12pm","1pm","2pm","3pm","4pm","5pm","6pm","7pm","8pm","9pm",
           "10pm","11pm")

weekdaysandhours <- as.vector(outer(weekdays, hours, paste))

outer会遍历weekdays的每个元素，依次和hours的所有元素执行paste操作，生成的矩阵转成向量后，自然就是「周一所有小时→周二所有小时→…→周日所有小时」的顺序。

方法2：使用expand.grid生成组合后处理 #

如果需要更灵活的后续操作（比如保留数据框格式），可以用expand.grid生成所有组合，再排序拼接：

weekdays <- c("Mon","Tue","Wed","Thu","Fri","Sat","Sun")
hours <- c("12am","1am","2am","3am","4am", "5am","6am","7am","8am","9am","10am",
           "11am","12pm","1pm","2pm","3pm","4pm","5pm","6pm","7pm","8pm","9pm",
           "10pm","11pm")

# 生成所有星期-小时组合的数据框
comb_df <- expand.grid(Weekday = weekdays, Hour = hours, stringsAsFactors = FALSE)
# 按原星期顺序排序（修正expand.grid默认的循环顺序）
comb_df <- comb_df[order(match(comb_df$Weekday, weekdays)), ]
# 拼接成目标向量
weekdaysandhours <- paste(comb_df$Weekday, comb_df$Hour)

这两种方法都避免了手动逐个拼接的冗余代码，当星期或小时列表需要修改时，只需调整原始向量即可，维护性大幅提升。

内容的提问来源于stack exchange，提问作者Chandler T