[R] How to plot two variables using a secondary Y axis

[Gabor Grothendieck]

We assume the Fo and Co represent the same data except in different
units (this seems to be approximately the case) so there is really
only one variable being measured here.  If that's not the case let
me know. Below we read the data, define enough padding around plot
to do what we want, call xyplot, draw the right axis and add the right
y lablel.

library(lattice)
library(grid)  # needed for grid.text

# data

Lines.raw <- "Date  Fo  Co
6/27/2007  57.1  13.9
6/28/2007  57.7  14.3
6/29/2007  57.8  14.3
6/30/2007  57  13.9
7/1/2007  57.1  13.9
7/2/2007  57.2  14.0
7/3/2007  57.3  14.1
7/4/2007  57.6  14.2
7/5/2007  58  14.4
7/6/2007  58.1  14.5
7/7/2007  58.2  14.6
7/8/2007  58.4  14.7
7/9/2007    58.7 14.8
"
# in reality next stmt would be DF <- read.table("myfile.dat", header = TRUE)
DF <- read.table(textConnection(Lines.raw), header = TRUE)
DF$Date <- as.Date(DF$Date, "%m/%d/%Y")

par.settings <- list(
	layout.widths = list(left.padding = 10, right.padding = 10),
	layout.heights = list(bottom.padding = 10, top.padding = 10)
)

xyplot(Co ~ Date, DF, default.scales = list(y = list(relation = "free")),
	ylab = "C", par.settings = par.settings)

trellis.focus("panel", 1, 1, clip.off = TRUE)
  pr <- pretty(DF$Fo)
  at <- 5/9 * (pr - 32)
  panel.axis("right", at = at, lab = pr, outside = TRUE)
  grid.text("F", x = 1.1, rot = 90) # right y axis label
trellis.unfocus()



On 7/10/07, Felipe Carrillo <mazatlanmexico at yahoo.com> wrote:
>          Date  Fo  Co    6/27/2007  57.1  13.9    6/28/2007  57.7  14.3    6/29/2007  57.8  14.3    6/30/2007  57  13.9    7/1/2007  57.1  13.9    7/2/2007  57.2  14.0    7/3/2007  57.3  14.1    7/4/2007  57.6  14.2    7/5/2007  58  14.4    7/6/2007  58.1  14.5    7/7/2007  58.2  14.6    7/8/2007  58.4  14.7    7/9/2007    58.7
>    14.8
>
>  Hello all:
>  I am a newbie to R, and I was wondering how can I plot the Temperature values above using Lattice or ggplot2 code. I want Date(X axis), Degrees F(Y axis) and Degrees C( on a secondary Y axis).
>  Thanks
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