josef.kar...@phila.gov wrote:
I am trying to plot 2 time series on the same graph.
For example, X1 is the vector of dates and times, its class is POSIXt. Y1
is an environmental parameter, e.g. salinity. X2 is a second vector of
dates and times, also of class POSIXt. X2 has a different length than
X1, but they have the exact same range. Y2 is another environmental
parameter, e.g. stream flow rate.
My approach is basically like this:
plot(X1,Y1)
par(xaxs = "r")
plot(X1, Y1)
par(new=TRUE)
plot(X2, Y2)
You probably want to use lines() to add the second time series if the
dates in X1 and X2 are not of identical range.
Uwe Ligges
the result is that the date tick marks for the second graph do not exactly
align with the first graph. This is because the second time series is
being slightly 'squeezed'; its timescale should match the first graph but
for some reason R is plotting it on a smaller scale.
The strange thing is that this doesn't happen for all time series I plot.
For example X3 and Y3 which have the same basic characteristics as X2 and
Y2, overlay perfectly with X1 and Y1. I don't know why it works for some
but not others.
I also tried setting xaxs to "i" -- and had the same outcome. Also had the
same outcome when trying either par(xaxs="i") or par(xaxs="r") after the
command par(new=TRUE)
Any insights would be appreciated
JK
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