[R] date and time data on x axis

[Bert Gunter]

See ?identify and ?locator

Cheers,
Bert

Bert Gunter

"The trouble with having an open mind is that people keep coming along and
sticking things into it."
-- Opus (aka Berkeley Breathed in his "Bloom County" comic strip )


On Sat, Nov 3, 2018 at 6:47 PM snowball0916 <snowball0916 using 163.com> wrote:

> Hi, Don
> After I've tried 1 month data. It show me like attachment.
>
> The problem is it's hard to identify the the high point from the graph.
> Is there possible, when my cursor move on some point , it will show me
> both x axis and y axis data?
> OR
> Is there other way to get the same goal?
>
> Thanks very much.
>
>
>
>
>
> From: MacQueen, Don
> Date: 2018-10-30 00:01
> To: snowball0916; r-help
> Subject: Re: [R] date and time data on x axis
> Here's an example of 24 hours of data at one second intervals.
>
> npts <- 24*60*60
>
> df <- data.frame(
>                  tm = seq( Sys.time(), by='1 sec', length=npts),
>                  yd = round(runif(npts),2)
>                  )
>
> head(df)
>
> with(df, plot(tm,yd))
>
> The x axis appears to me to be displayed in a neat and clean way. I don't
> understand what the problem is.
> (The data itself is illegible, but that's a different problem.)
>
> The default axis may not be what you want, but it is neat and clean. To
> choose the axis tick marks and labels yourself, use axis() or axis.POSIXct,
> as Rui mentioned.  help(axis.POSIXct) provides examples of actual use.
>
> I prefer to do as much as possible with base R, so look at this example:
>
> > as.POSIXct( '20181028_10:00:00' , format='%Y%m%d_%H:%M:%S')
> [1] "2018-10-28 10:00:00 PDT"
>
> Therefore
>   xdata <- as.POSIXct(mydata$V1, format='%Y%m%d_%H:%M:%S')
> is perfectly adequate (the lubridate package is not essential here)
>
>
> par() is the function that sets graphical parameters. There are many
> graphical parameters.
> "mar" is the parameter that specifies the sizes of the plot margins  ( see
> ?par )
>
> This expression
>    op <- par(mar = c(4, 0, 0, 0) + par("mar"))
> is a way to modify the values of the "mar" parameter.
>
> Type the following commands
>    par('mar')
>    par()$mar        ## an alternative
>    c(4,0,0,0) + par('mar')
>    par(mar = c(4, 0, 0, 0) + par("mar"))
>    par('mar')        ## to see that the margins have been changed
>
> --
> Don MacQueen
> Lawrence Livermore National Laboratory
> 7000 East Ave., L-627
> Livermore, CA 94550
> 925-423-1062
> Lab cell 925-724-7509
>
> On 10/28/18, 8:16 AM, "R-help on behalf of snowball0916" <
> r-help-bounces using r-project.org on behalf of snowball0916 using 163.com> wrote:
>
>     Hi, guys
>     How do you guys deal with the date and time data on x axis?
>     I have some trouble with it. Could you help with this?
>
>     =============
>     Sample Data
>     =============
>     The sample data look like this:
>
>     20181028_10:00:00 600
>     20181028_10:00:01 500
>     20181028_10:00:02 450
>     20181028_10:00:03 660
>     ......
>
>     =============
>     My Code
>     =============
>
>     library(lubridate)
>     mydata <- read.table("e:/R_study/graph_test2.txt")
>     xdata <- ymd_hms(mydata$V1)
>     ydata <- mydata$V2
>     plot(xdata, ydata, type="o")
>
>
>     =============
>     Questions:
>     =============
>
>     1. Why my x axis does not show me the correct date time like
> ""2018-10-28 10:00:00 UTC" ?
>     2. If my data is very huge(like data in every second and the data has
> the whole day , even the whole month), how can I display the x axis in a
> neat and clean way?
>
>     Thanks very much.
>
>
>
>
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>
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>
>
> ______________________________________________
> R-help using r-project.org mailing list -- To UNSUBSCRIBE and more, see
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>

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