[R] How to create multi-panels plots with scatterplot/xyplot and POSIX time objects?

Question

Hi!

A newbie question. (ADDED NEW INFO)

I have a set of time stamped data that were collected randomly. I like to create a matrix of plots, but I could not create using either scatterplot or xyplot & time objects.

my data

dataset$Time  #POSIX time objects (no set sampling period)
              #i built POSIX time objects by dataset$Time<-strptime(tt, "%H:%M:%OS")
              #the origial string was formated like this 12:12:12.234 (HH:MM:SS:msec)
dataset$d1, dataset$d2 #integers
dataset$d3 #factor with 10 levels

.

i can do these

plot( dataset$Time, dataset$d1)
scatterplot(dataset$d1 ~ dataset$d2 | dataset$d3, data=dataset)
xyplot(dataset$d1 ~ dataset$d2 | dataset$d3, data=dataset)

However, i can NOT do these (POSIX time object in x-axis)

scatterplot(dataset$d1 ~ dataset$Time | dataset$d3, data=dataset)
xyplot(dataset$d1 ~ dataset$Time | dataset$d3, data=dataset)

(NEW INFO)

Error in structure(.Internal(as.POSIXct(x, tz)), class = c("POSIXt", "POSIXct"), : invalid 'x' argument.

(NEW INFO) but this works (POSIX time object in y-axis)

xyplot(dataset$Time ~ dataset$d1 | dataset$d3, data=dataset)

related, but different question is hexbin. When time objects are added to hexbin, the plot from the hexbin does not show correct time format on the units.

bin<-hexbin(dataset$Time, dataset$d1) 
plot(bin))

What should I do?

Thanks for looking into it!!

Answer 1

Apparently R has some problem dealing with addiction of POSIX times... it gives me the error:

Error in +.POSIXt(x[floor(d)], x[ceiling(d)]) : binary '+' is not defined for "POSIXt" objects

just cast them to numeric and it should work. You can hide the corresponding axis and redraw it later with the correct dates

E.g.:

scatterplot(dataset$d1 ~ as.numeric(dataset$Time) | dataset$d3, data=dataset, xaxt="n")
axis(1, at=as.numeric(dataset$Time), labels=dataset$Time, cex.axis=0.5)

Answer 2

For me it just works, so you probably has a time vector in a bad format. What do you get when you call class(dataset$Time)? It should contain "POSIXct" for this to work.

On the other hand, you don't need to put dataset$ in formula if you supply data=dataset.

Answer 3

Here is a working example. You may have gotten your data formats wrong -- one needs to be careful about the precise data formats.

First, a simple data frame:

R> X <- data.frame(pt=Sys.Date()+0:4, x1=100+cumsum(rnorm(5)),
+                                     x2=90+cumsum(rt(5,4)))
R> X
          pt     x1    x2
1 2010-06-22  98.73 90.33
2 2010-06-23  99.43 89.56
3 2010-06-24  98.85 86.95
4 2010-06-25  99.08 88.52
5 2010-06-26 100.30 94.08
R> 

This is so-called wide form which lattice does not use. You need to transform it into long format. I use stack() here, you can also use cast() and melt() from the reshape package:

R> Y <- data.frame(pt=rep(X$pt,2), stack(X, select=c(x1,x2)))
R> Y
           pt values ind
1  2010-06-22  98.73  x1
2  2010-06-23  99.43  x1
3  2010-06-24  98.85  x1
4  2010-06-25  99.08  x1
5  2010-06-26 100.30  x1
6  2010-06-22  90.33  x2
7  2010-06-23  89.56  x2
8  2010-06-24  86.95  x2
9  2010-06-25  88.52  x2
10 2010-06-26  94.08  x2
R> 

Now the xyplot call is simply:

R> xyplot(values ~ pt | ind, data=Y, panel=panel.lines)

and you can of course use much more complicated conditioning expressions.