[R] ts; decompose; plot and title

[Gavin Simpson]

On Tue, 2007-02-27 at 15:24 -0200, Alberto Monteiro wrote:
> Is there any way to give a "decent" title after I plot something
> generated by decompose?
> 
> For example:
> 
> # generate something with period 12
> x <- rnorm(600) + sin(2 * pi * (1:600) / 12)
> 
> # transform to a monthy time series
> y <- ts(x, frequency=12, start=c(1950,1))
> 
> # decompose
> z <- decompose(y)
> 
> # plot
> plot(z)
> 
> Now, the title is the ugly "Decomposition of additive time series".
> How can do this with a decent title, like "Analysis of UFO abductions"?
> 
> Alberto Monteiro

It is because plot.decompose.ts decides to impose it's own title for
some reason (using getAnywhere(plot.decompose.ts) to get the function
definition):

function (x, ...)
{
    plot(cbind(observed = x$random + if (x$type == "additive")
        x$trend + x$seasonal
    else x$trend * x$seasonal, trend = x$trend, seasonal = x$seasonal,
        random = x$random), main = paste("Decomposition of",
        x$type, "time series"), ...)
}

I'd just write your own wrapper instead, using plot.decompose.ts, along
the lines of:

decomp.plot <- function(x, main = NULL, ...)
{
    if(is.null(main))
	main <- paste("Decomposition of", x$type, "time series")
    plot(cbind(observed = x$random + if (x$type == "additive")
        x$trend + x$seasonal
    else x$trend * x$seasonal, trend = x$trend, seasonal = x$seasonal,
        random = x$random), main = main, ...)
}

#then to complete your example:

# generate something with period 12
x <- rnorm(600) + sin(2 * pi * (1:600) / 12)

# transform to a monthy time series
y <- ts(x, frequency=12, start=c(1950,1))

# decompose
z <- decompose(y)

# plot
decomp.plot(z, main = "Analysis of UFO abductions")

Perhaps you could also file a bug report under the wish list category,
showing your example and the fact that

plot(z, main = "Analysis of UFO abductions") 

gives this error:

Error in plotts(x = x, y = y, plot.type = plot.type, xy.labels =
xy.labels,  :
        formal argument "main" matched by multiple actual arguments

It isn't really a bug, but an infelicity in the way the function
currently works - my decomp.plot function may even be a suitable patch
or maybe the following is better:

decomp.plot2 <- function(x, main, ...)
{
    if(missing(main))
	main <- paste("Decomposition of", x$type, "time series")
    plot(cbind(observed = x$random + if (x$type == "additive")
        x$trend + x$seasonal
    else x$trend * x$seasonal, trend = x$trend, seasonal = x$seasonal,
        random = x$random), main = main, ...)
}

HTH

G

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 Gavin Simpson                 [t] +44 (0)20 7679 0522
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