Le 22/02/2021 à 18:01, Deepayan Sarkar a écrit :
On Mon, Feb 22, 2021 at 9:56 PM Laurent Rhelp <[email protected]> wrote:Dear R-Help-List,I have to process time series with a sampling frequency of 1 MHz. I use the POSIXct format for the date-times with microsecond in a zoo object and the xyplot.zoo function to do the graphs. As I show in the below example I had a trouble to plot the labels on the x-axis with an error message. I found a solution but I would like to know if I miss something. The link https://stackoverflow.com/questions/7726034/how-r-formats-posixct-with-fractional-seconds helped me to understand how to print the POSIXct value to see the microseconds thanks to the function myformat.POSIXct: myformat.POSIXct <- function(x, digits=6) { x2 <- round(unclass(x), digits) attributes(x2) <- attributes(x) x <- as.POSIXlt(x2,origin="1970-01-01",tz="GMT") x$sec <- round(x$sec, digits) format.POSIXlt(x, paste("%Y-%m-%d %H:%M:%OS",digits,sep=""),tz="GMT") } ## The example giving the error message: library(lattice) library(zoo) ## options(digits = 16) # to see all the digits on the screen options(digits.secs = 6) # to see the microseconds # mock data # a sine with a frequency f0 and two others with a delay Fs <- 1e+6 # sampling frequency 1 MHz Ts <- 1/Fs # frequency of the sinus f0 <- 100000 t0 <- 1/f0 time <- seq(0, length = 1000, by = Ts) A1 <- 1 y1 <- A1 * sin(2*pi*f0*time) y2 <- 2 * A1 * sin(2*pi*f0*(time+0.000002)) y3 <- 3 * A1 * sin(2*pi*f0*(time+0.000005)) ## creation of a dataframe: ## DF <- data.frame( time = time, y1 = y1, y2 = y2, y3 = y3) # Since I want to allow for the datetime POSIXct format on the x-axis # for the plot I transform my dataframe in a zoo object # # say that my acquisition began at "2021-02-08 09:15:50.000000" # mystart <- as.POSIXct("2021-02-08 09:15:50.000000", format = "%Y-%m-%d %H:%M:%OS",tz="GMT") mystart # To see the correct datetime I use the myformat.POSIXct function myformat.POSIXct(mystart) ## ## using the method seq.POSIXct as following doesn't work: ## mydatetime <- seq( mystart , length = nrow(DF), by = "0.000001 sec") ## head( myformat.POSIXct(mydatetime) ) ## if I use the following command it works: mydatetime <- seq( mystart , length = nrow(DF), by = 0.000001) head( myformat.POSIXct(mydatetime) ) ## I do the zoo object: DF.z <- zoo(DF[,-1],order.by = mydatetime) ## We don't see the correct value for the index: head(DF.z) # time y1 y2 y3 # 2021-02-08 09:15:50.000000 0e+00 0.000000000000000e+00 1.902113032590307e+00 3.673819061467132e-16 # 2021-02-08 09:15:50.000000 1e-06 5.877852522924730e-01 1.902113032590307e+00 -1.763355756877419e+00 # 2021-02-08 09:15:50.000001 2e-06 9.510565162951535e-01 1.175570504584947e+00 -2.853169548885460e+00 # 2021-02-08 09:15:50.000003 3e-06 9.510565162951536e-01 1.133099690464601e-15 -2.853169548885460e+00 # 2021-02-08 09:15:50.000004 4e-06 5.877852522924736e-01 -1.175570504584946e+00 -1.763355756877420e+00 # 2021-02-08 09:15:50.000005 5e-06 5.665498452323003e-16 -1.902113032590306e+00 -3.399299071393802e-15 # If I use myformat.POSIXct I see that the index is correct in the object DF: head(myformat.POSIXct(index(DF.z))) ## and when I plot I have an error: xyplot( DF.z , screens = c(1,1,1) , type = "l" , col = c("red","blue","black") ) # Error in prettyDate_TMP(x, ...) : range too small for min.nAt least the immediate problem is that lattice:::prettyDate_TMP(range(mydatetime)) # Error in lattice:::prettyDate_TMP(range(mydatetime)) : # range too small for min.n grDevices:::prettyDate(range(mydatetime)) # [1] "2021-02-08 09:15:48 GMT" "2021-02-08 09:15:49 GMT" # [3] "2021-02-08 09:15:50 GMT" "2021-02-08 09:15:51 GMT" # [5] "2021-02-08 09:15:52 GMT" "2021-02-08 09:15:53 GMT" So the version in lattice (which was supposed to be a temporary stopgap till R 2.12 was released) has not kept up. I will fix. Does the output above look OK to you?
It is ok for me except the fact that I would like to see on the x-axis labels the fractional seconds, at least the milliseconds.
Best, -Deepayan# if I process by hand the plot of the labels on the x-axis it works: # myend <- tail(mydatetime,1) myticks <- seq( mystart , to = myend , length = 5) mylabels <- format(myticks,"%H:%M:%OS") xyplot( DF.z , screens = c(1,1,1) , type = "l" , col = c("red","blue","black") , scales = list( y= list(relation = "free", abbreviate=TRUE), x = list( at = myticks, labels = mylabels , rot = 45, cex = 0.5) ) ) # The microseconds are well taken into account with the window function # if I want to plot only 100 microseconds but there is of course the same # trouble for the plot myend <- as.POSIXct("2021-02-08 09:15:50.000100", format = "%Y-%m-%d %H:%M:%OS",tz="GMT") myformat.POSIXct(myend) DF.w <- window( DF.z ,start = mystart, end = myend) myticks <- seq( mystart , to = myend , length = 5) mylabels <- format(myticks,"%H:%M:%OS") xyplot( DF.w , screens = c(1,1,1) , type = "l" , col = c("red","blue","black") ) ## Error in prettyDate_TMP(x, ...) : range too small for min.n xyplot( DF.w , screens = c(1,1,1) , type = "l" , col = c("red","blue","black") , scales = list( y= list(relation = "free", abbreviate=TRUE), x = list( at = myticks, labels = mylabels , rot = 45, cex = 0.5) ) ) May you please tell me if I miss something in the way to use POSIXct with microseconds in a zoo object ? Thank you Laurent -- L'absence de virus dans ce courrier électronique a été vérifiée par le logiciel antivirus Avast. https://www.avast.com/antivirus ______________________________________________ [email protected] 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.
-- L'absence de virus dans ce courrier électronique a été vérifiée par le logiciel antivirus Avast. https://www.avast.com/antivirus ______________________________________________ [email protected] 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.
