[R] How to plot dates

[Daniel Nordlund]

On 3/16/2021 3:32 PM, Gregory Coats via R-help wrote:
> Thank you. Let me redefine the situation.
> Each time an event starts, I record the date and time.
> Each day there are 4 new events. Time is the only variable.
> I would like to graphically show how the time for events 1, 2, 3, and 4 for the current day compare to the times for events 1, 2, 3, and 4 for the previous day. How would I plot / display those times differences?
> Greg Coats
>
> library (ggplot2)
> myDat <- read.table(text =
> "datetime
> 2021-03-12 05:16:46
> 2021-03-12 09:17:02
> 2021-03-12 13:31:43
> 2021-03-12 22:00:32
> 2021-03-13 09:21:43
> 2021-03-13 13:51:12
> 2021-03-13 18:03:13
> 2021-03-13 22:20:28
> 2021-03-14 08:59:03
> 2021-03-14 13:15:56
> 2021-03-14 17:25:23
> 2021-03-14 21:36:26",
> sep = ",", header = TRUE)
> head(myDat)
> myDat$datetime <- as.POSIXct(myDat$datetime, tz = "", format ="%Y-%M-%d %H:%M:%OS")
>
>> On Mar 16, 2021, at 3:34 PM, John Fox <jfox using mcmaster.ca> wrote:
>>
>> Dear Greg,
>>
>> Coordinate plots typically have a horizontal (x) and vertical (y) axis. The command
>>
>> 	ggplot(myDat, aes(x=datetime, y = datetime)) + geom_point()
>>
>> works, but I doubt that it produces what you want.
>>
>> You have only one variable in your data set -- datetime -- so it's not obvious what you want to do. If you can't clearly describe the structure of the plot you intend to draw, it's doubtful that I or anyone else can help you.
>>
>> Best,
>> John
>>
>> John Fox, Professor Emeritus
>> McMaster University
>> Hamilton, Ontario, Canada
>> web: https://socialsciences.mcmaster.ca/jfox/ <https://socialsciences.mcmaster.ca/jfox/>
> 	[[alternative HTML version deleted]]
>
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I am only guessing about what you are looking for by way of a visual 
comparison.  Here is one way of visualizing the variation of event times

library (ggplot2)
myDat <- read.table(text =
"datetime
2021-03-12 05:16:46
2021-03-12 09:17:02
2021-03-12 13:31:43
2021-03-12 22:00:32
2021-03-13 09:21:43
2021-03-13 13:51:12
2021-03-13 18:03:13
2021-03-13 22:20:28
2021-03-14 08:59:03
2021-03-14 13:15:56
2021-03-14 17:25:23
2021-03-14 21:36:26",
sep = ",", header = TRUE)

# create datepart variable - dte
myDat$dte <- as.Date(myDat$datetime, "%m/%d/%Y", tz='')

# create timepart variable - tme
library(lubridate)
myDat$tme <- hms::hms(as.numeric(myDat$datetime - 
floor_date(myDat$datetime, "1 day"), unit="secs"))

# plot event date by time grouped by date
ggplot(myDat, aes(x=tme, y = dte, group = dte)) + geom_line() + 
geom_point() +
       expand_limits(y=as.Date(c('20210301', '20210331'),'%Y%m%d'))

If this doesn't help get you started, you need to provide a description 
of what you want your plot to look like.

Dan

-- 
Daniel Nordlund
Port Townsend, WA  USA