【每天一个R语言命令】-strptime/strftime

【准备】
R中有专门的时间格式数据，ts(time series)。
比如：

> class(presidents)
[1] "ts"
> class(airmiles)
[1] "ts"

【描述】

The strptime function converts characters to time objects.
The strftime function converts time objects to characters.
【用法】
strptime(x, format=', tz='', ...)
【参数】
x代表字符，format代表格式，tz代表time zone
【代码】

> Sys.time()
[1] "2021-01-31 11:42:31 CST" #sct也就是中国的时间

> time_1 <- "2021-01-31"   
> class(time_1)
[1] "character"

> time_2 <- strptime(time_1, format = '%Y-%m-%d')
> class(time_2)
[1] "POSIXlt" "POSIXt"

time_3 <- "2020-06-01 16:15:10"
> time_3a <- strptime(time_3,                              # Apply strptime with timezone
+                     format = "%Y-%m-%d %H:%M:%OS",
+                     tz = "") #当前时区省略不写
> time_3a
[1] "2020-06-01 16:15:10 CST"

# 生成日期
> seq(as.Date('2020-02-01'),as.Date('2020-02-10'), by=1)
 [1] "2020-02-01" "2020-02-02" "2020-02-03" "2020-02-04" "2020-02-05" "2020-02-06" "2020-02-07" "2020-02-08"
 [9] "2020-02-09" "2020-02-10"
# 生成时间序列
> sales <- round(runif(20, min = 50, max = 100))
> ts(sales, start = c(2000,1), end = c(2020,12), frequency = 1)
Time Series:
Start = 2000 
End = 2031 
Frequency = 1 
 [1] 56 53 85 82 77 88 76 81 80 67 92 97 76 82 68 55 78 72 69 73 56 53 85 82 77 88 76 81 80 67 92 97