How can I plot with 2 different y-axes in R with DATE on X axis?

Question

Basically the question is the same as this one: How can I plot with 2 different y-axes? except that I have a date on the x axis and pretty(range()) doesn't work for me using dates.

(sorry I don't have enough "reputation" to comment the above question to ask for more info so I need to start a new question).

I wrote the following function:

  PvsRef<-function(id,feature){
  ymax= max(data[[feature]], na.rm=TRUE)
  plotdata = data[data$ID==id,]

  plot(plotdata$date,plotdata$ref, type="l", col="red", axes=FALSE, ylim=c(0,48), main=paste0("Reference vs.",feature), sub=as.character(id),  xlab="", ylab="")
  axis(2, ylim=c(0,48),col="red",las=1)
  mtext("Reference",side=2,col="red",line=2.5)
  box()

  par(new=TRUE)

  plot(plotdata$date,plotdata[[feature]], type="b", col="blue", axes=FALSE, ylim=c(0,ymax),  xlab="", ylab="")
  mtext(feature,side=4,col="blue",line=4) 
  axis(4, ylim=c(0,ymax), col="blue",col.axis="blue",las=1)

  axis(1,pretty(range(plotdata$date),10))
  mtext("Date",side=1,col="black",line=2.5)  


  axis(1,pretty(range(plotdata$date),10))
  mtext("Date",side=1,col="black",line=2.5)  


  }

the x-axis however shows weird numbers instead of dates.

example data:

data = data.frame(ID=c(1,1,1,1,1,1), date=as.Date(c("2000-01-01","2000-02-01","2000-03-01","2000-04-01","2000-05-01","2000-06-01")), ref=c(30,23,43,12,34,43), other=c(120,140,230,250,340,440))

then I want to run the function using

PvsRef(1,"other")

but no proper x-axis appears.

EDIT:

if instead I use

  axis.Date(1,pretty(range(plotdata$date),10))
  mtext("Date",side=1,col="black",line=2.5)

proper dates show up, but there isn't 10 ticks as demanded by pretty.

Did you run the code that creates the example data in your question? It doesn't run. You need to pass a character vector to `as.Date(...)` to create Dates this way. Also, `other=(...)` is syntactically incorrect. — jlhoward, Dec 03 '14 at 20:29
so by using axis.Date instead of axis I can get normal looking dates, but it doesn't give the number of ticks specified in pretty. — patapouf_ai, Dec 03 '14 at 20:31
hey jlhoward. thanks. indeed you are right. above I forgot to put the quotes arround the dates and the c in other. let me see if I can edit that. — patapouf_ai, Dec 03 '14 at 20:32
I try to use pretty.Date but that just gives me the error that it can't find pretty.Date — patapouf_ai, Dec 03 '14 at 20:42
`pretty.Date` [is in the `grDevices` package](http://www.rdocumentation.org/advanced_search?utf8=%E2%9C%93&q=&package_name=&function_name=pretty.Date&title=&description=&author=). So load that... — Gregor Thomas, Dec 03 '14 at 20:49
Thanks @Gregor . I have grDevices loaded. But it still gives me that error. If I just use pretty on the dates it doesn't give any errors. It looks like pretty.Date can't be called directly but must be called from the wrapper pretty? — patapouf_ai, Dec 03 '14 at 21:29
Yeah, looks like you're correct. Calling `grDevices:::pretty.Date()` is equivalent to `pretty()` on a `Date` object. Why were you trying to call `pretty.Date()` directly? — Gregor Thomas, Dec 03 '14 at 21:38
because calling pretty is not giving me the desired outcome ... and because that trick helped with axis. — patapouf_ai, Dec 03 '14 at 22:13

jbaums · Accepted Answer · 2014-12-04T10:48:34.687

For axis.Date, you need to specify the argument name at when setting the tick/label positions. If you fail to do this, axis.Date treats the second argument as x, which results in a suitable grid of labels being chosen (see ?axis.Date).

Changing that line to, for example:

axis.Date(1, at=pretty(range(plotdata$date), 10), format='%d %b', las=2, 
          cex.axis=0.8)`

yields the 10 ticks you are looking for. However, the intervals are inconsistent. Perhaps it might be better to specify a date sequence, such as:

seq(min(plotdata$date), max(plotdata$date), length.out=10)

So your function could be adjusted to:

f <- function(id, feature) {
  opar <- par()
  on.exit(suppressWarnings(par(opar)))
  par(mar=c(6, 4, 4, 5))
  ymax <- max(data[[feature]], na.rm=TRUE)
  plotdata <- data[data$ID==id,]

  plot(plotdata$date, plotdata$ref, type="l", col="red", axes=FALSE, 
       ylim=c(0, 48), main=paste0("Reference vs.", feature), 
       sub=as.character(id), xlab="", ylab="")
  mtext("Reference", side=2, col="red", line=2.5)
  axis(2, ylim=c(0, 48), col='red', col.axis="red", las=1)

  par(new=TRUE)  
  plot(plotdata$date, plotdata[[feature]], type="b", col="blue", axes=FALSE, 
       ylim=c(0,ymax),  xlab="", ylab="")
  mtext(feature, side=4, col="blue", line=3) 
  axis(4, ylim=c(0, ymax), col="blue", col.axis="blue", las=1)

  axis.Date(1, at=seq(min(plotdata$date), max(plotdata$date), length.out=10), 
            format='%d %b', las=2, cex.axis=0.8)
  box(lwd=2)
}  

f(1, 'other')

enter image description here

Thank you! That is exactly what I was looking for! Sorry I can't upvote you yet because I don't have enough reputation, I'll do it once I'm able to. — patapouf_ai, Dec 05 '14 at 12:55

How can I plot with 2 different y-axes in R with DATE on X axis?

1 Answers1