如何在R中以日期和时间为x轴进行绘制

Question

大家好，我一直在尝试绘制一些数据，其中x轴为某天的时间，y轴为某路段的自由流动速度的数值。 下面显示了部分数据的简单示例

> mydf1
# A tibble: 11 x 3
   Date_UTC   Time     Free_Flow_Speed
   <date>     <chr>              <dbl>
 1 2019-05-07 08:15:00           81.0 
 2 2019-05-07 08:30:00            9.36
 3 2019-05-07 08:45:00            4.15
 4 2019-05-07 09:00:00            7.18
 5 2019-05-07 09:15:00            9.78
 6 2019-05-07 09:30:00           16.4 
 7 2019-05-07 09:45:00           97.9 
 8 2019-05-07 10:00:00          101.  
 9 2019-05-07 10:15:00          101.  
10 2019-05-07 10:30:00          102.  
11 2019-05-07 10:45:00          100.  

我通过使用以下命令转换“ Date_UTC”来创建“时间”

mydf1$Time <- format(as.POSIXct(data2$`UTC Date and Time`), format = "%H:%M:%S")

我试图在x轴上绘制“时间”，在y轴上绘制“ Free_Flow_Speed”：

> plot(mydf1$Time, mydf1$Free_Flow_Speed)
Error in plot.window(...) : need finite 'xlim' values
In addition: Warning messages:
1: In xy.coords(x, y, xlabel, ylabel, log) : NAs introduced by coercion
2: In min(x) : no non-missing arguments to min; returning Inf
3: In max(x) : no non-missing arguments to max; returning -Inf

我尝试研究一下，很显然，时间被转换为仅“ NA”，可能是因为“时间”为“字符”，而“ Free_Flow_Speed”为“双精度/数字”

> str(mydf1)
Classes ‘tbl_df’, ‘tbl’ and 'data.frame':   11 obs. of  3 variables:
 $ Date_UTC       : Date, format: "2019-05-07" "2019-05-07" "2019-05-07" "2019-05-07" ...
 $ Time           : chr  "08:15:00" "08:30:00" "08:45:00" "09:00:00" ...
 $ Free_Flow_Speed: num  80.99 9.36 4.15 7.18 9.78 ...

我试图将“ Free_Flow_Speed”转换为“ Char”，但无济于事。

>mydf1 <- as.numeric(as.character(mydf1$Free_Flow_Speed))
Error in mydf1$Free_Flow_Speed : $ operator is invalid for atomic vectors

> mydf2 <- c(mydf1$Time, as.numeric(as.character(mydf1$Free_Flow_Speed)))

dput（数据）

> dput(mydf1)
structure(list(Date_UTC = structure(c(18023, 18023, 18023, 18023, 
18023, 18023, 18023, 18023, 18023, 18023, 18023), class = "Date"), 
    Time = c("08:15:00", "08:30:00", "08:45:00", "09:00:00", 
    "09:15:00", "09:30:00", "09:45:00", "10:00:00", "10:15:00", 
    "10:30:00", "10:45:00"), Free_Flow_Speed = c(80.99, 9.36, 
    4.15, 7.18, 9.78, 16.37, 97.91, 100.54, 100.81, 102.46, 100.27
    )), row.names = c(NA, -11L), class = c("tbl_df", "tbl", "data.frame"
))

我希望有人可以阐明如何使用“时代”作图。 在excel中这是可行的，但是我正在尝试使用该数据集探索ggplot2，并且希望能够意识到我做错了什么。

提前致谢！

Answer 1

你的线

mydf1$Time <- format(as.POSIXct(data2$`UTC Date and Time`), format = "%H:%M:%S")

特别

data2$`UTC Date and Time`您提供的输入数据不对应。

正确的转换可以通过首先将日期和小时粘贴在一起然后转换：

df1 <- df1 %>% mutate(all_date=as.POSIXct(paste(Date_UTC,Time),format = "%Y-%m-%d %H:%M:%S"))

最后，将其绘制：

plot(df1$all_date,df1$Free_Flow_Speed)