Gaps in plotting temporal data.

I'm trying to plot some temporal data that have some gaps in them. You
can see the plot here: http://www.tiikoni.com/tis/view/?id=da222e2.

The problem is that during the time gaps in the TS the line plot is
interpolated over the gap and I don't want it to. I've tried
interleaving the gaps with an NA flag, but there are around 10000
data-points sorted from multiple files, that makes it difficult to add
the NA flag manually. If it's not possible to define the behaviour of
the plot(0function, is there another plot I can use, e.g. zoo, that will
allow me to not have the lines drawn between the gaps?

Any software is going to have the same problem you had:  how do you 
define a gap?  If the definition is something simple like "time 
difference greater than X", then it will be fairly easy:  use diff() to 
find all the time differences in the sorted times, and wherever those 
exceed X, insert a new data point with an NA value.  For example,

t <- c(1,2,3,7,8,9,11,12,13)
x <- rnorm(length(T))
d <- diff(t)
gap <- which(d > 1.5)
if (length(gap)) {
   newT <- (t[gap] + t[gap+1])/2
   t <- c(t, newT)
   x <- c(x, rep(NA, length(newT)))
   o <- order(t)
   t <- t[o]
   x <- x[o]
}
plot(t, x, type='l')

Duncan Murdoch

If you're in a hurry, it's way easier than that:

t <- c(1,2,3,7,8,9,11,12,13)
x <- rnorm(length(t))

new.t <- min(t):max(t)
new.x <- NULL
new.x[t-min(t)+1] <- x

plot(new.t, new.x, type='l')

This is wastes max(t)-min(t)-length(t)+1 vector entries, but presumably you won't be wasting a lot of real estate along the horizontal axis of a plot.  If you do, you're going to need to fix that anyway.



-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] On Behalf Of Duncan Murdoch
Sent: Thursday, February 24, 2011 8:45 AM
To: Christos Delivorias
Cc: r-help at r-project.org
Subject: Re: [R] Gaps in plotting temporal data.

I'm trying to plot some temporal data that have some gaps in them. You
can see the plot here: http://www.tiikoni.com/tis/view/?id=da222e2.

The problem is that during the time gaps in the TS the line plot is
interpolated over the gap and I don't want it to. I've tried
interleaving the gaps with an NA flag, but there are around 10000
data-points sorted from multiple files, that makes it difficult to add
the NA flag manually. If it's not possible to define the behaviour of
the plot(0function, is there another plot I can use, e.g. zoo, that will
allow me to not have the lines drawn between the gaps?

Any software is going to have the same problem you had:  how do you
define a gap?  If the definition is something simple like "time
difference greater than X", then it will be fairly easy:  use diff() to
find all the time differences in the sorted times, and wherever those
exceed X, insert a new data point with an NA value.  For example,

t <- c(1,2,3,7,8,9,11,12,13)
x <- rnorm(length(T))
d <- diff(t)
gap <- which(d > 1.5)
if (length(gap)) {
   newT <- (t[gap] + t[gap+1])/2
   t <- c(t, newT)
   x <- c(x, rep(NA, length(newT)))
   o <- order(t)
   t <- t[o]
   x <- x[o]
}
plot(t, x, type='l')

Duncan Murdoch

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