From: Ken <katakagi_at_bu.edu>

Date: Mon, 16 May 2011 15:33:31 +0000

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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. Received on Mon 16 May 2011 - 15:35:56 GMT

Date: Mon, 16 May 2011 15:33:31 +0000

Pablo Rosado <pablojrosado <at> lbl.gov> writes:

*>
**> Hi,
**>
*

> I am plotting data in which the x values are a timestamp. I am trying to

*> change the x-ticks so they will be in specified hours of the day, but it
**> always start from hour 4 of the day. And I need it to start from the
**> beginning of the axis (at x=0) and then each tick be on the interval I
**> specify.
**>
**> Here is my plotting script:
**>
**> *##-- ROOF COMPARISON - SOUTH--
**> win.graph()
**> plot(x=tiempo,y=timeframe[,8],xlab="",ylab="",**xaxt='n',**
**> yaxt='n',type="l",col="blue",lwd=3,ylim=c(0,80),font=2,las=1)
**> axis(side=1,at=seq(0,24,3))
**> axis(side=2,at=seq(0,80,10),line=NA, tcl = -0.5,font=2,las=1)
**> lines(x=tiempo,y=timeframe[,47],col="red",lwd=3)
**> title(xlab=paste("Local Standard Time (",date), cex.lab=1,font.lab=2)
**> title(ylab="Temperature (°C)", cex.lab=1,font.lab=2)
**> legend("topleft",legend=c("cool", "standard"),col=c("blue",
**> "red"),lwd=c(4,4),bty="n",cex=1.25)
**> grid(nx=NULL,ny=NULL,col = "gray", lty = "dotted",lwd = 1)*
**>
**> But with the axis(side=1...) nothing appears.
**>
**> I have been practicing with the following code to change the xaxis but it
**> says that x and y lengths differ:
**>
**> *## TIMESTAMP IS A ONE COLUMN VECTOR IN WHICH I SAVED THE TIMESTAMP FROM MY
**> FILE
**> string.to.time <-
**> function(timestamp)
**> strptime(x=timestamp, format="%Y-%m-%d %H:%M:%S")
**>
**> decimal.day <-
**> function(timestamp) {
**> y <- as.POSIXlt(**timestamp**)
**> y$day + y$hour/24 + y$min/(24*60) + y$sec/(24*60*60)
**> }
**>
**> decimal.hour <-
**> function(**timestamp**) {
**> dd <- decimal.day(**timestamp**)
**> 24 * (dd - floor(dd))
**> }
**>
**> ##create some data to plot
**> t.start <- string.to.time("2011-05-02 00:00:00")
**> t.start
**> t.vector <- t.start + (0:24)*3600
**> t.vector
**> z.vector <- 1:length(t.vector)
**> z.vector
**>
**> ##vector of decimal hours
**> dh.vector <- decimal.hour(t.vector)
**> dh.vector
**>
**> plot(x=dh.vector, y=z.vector, xlim=c(0,24), xaxt="n", xlab="Hour of day",
**> ylab="Some property")
**> *
**>
**> Thank You so much and have a great weekend.
**>
*

Hi Pablo,

I'm a big fan of the "chron" package for plotting dates on axis. Not sure if this is what you are looking for,but might be helpful. Here is a simple example using the chron package and plotting dates on x-axis. You can alter the text labels on x-axis using substr() on the date vector.

# create "chron" time vector

library(chron)

excel.dates <- seq(40179.0 + 1/6, 40180.0 + 1/6, 1/6)
orig <- chron("12/30/1899")

date.time <- orig + excel.dates;

time.only <- substr(date, 11, 18)

# Y data

y.dat = rnorm(7, 10, 3)

# Plot it up! Don't add annotations or axes for now plot(date.time, y.dat, type="n", ann=F, axes=F)

# Add data

lines(date.time, y.dat, lwd = 2, col = "black")
points(date.time, y.dat, pch = 20, col = "magenta")
box() # add box around plot

# Add X-Axis and label

axis(1, at=c(seq(date.time[1], date.time[length(date.time)],1/6)), tck = +0.01,
labels = F)

#label=date.time # prints date and time

label = time.only # only prints time

x.len=length(label)

text(x=date.time[1:x.len], par("usr")[3]-.135, srt = 45, adj = 1,

labels = label, xpd = T)

mtext(side = 1, "Time", line = 3.2) #X-axis label

**HTH,
**

Ken

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