[R] using spec.pgram

From: Anthony Mathelier <anthony.mathelier_at_gmail.com>
Date: Mon, 09 Jun 2008 20:52:46 +0200


Hi everyone,

first of all, I would like to say that I am a newbie in R, so I apologize in advance if my questions seem to be too easy for you.

Well, I'm looking for periodicity in histograms. I have histograms of certain phenomenons and I'm asking whether a periodicity exists in these data. So, I make a periodogram with the function spec.pgram. For instance, if I have a histogram h, I call spec.pgram by spec.pgram (h, log="no", taper=0.5). So, I have some peaks that appear and I would like to interpret them but I do not know how they are computed and so what a peak with a value of 10000 represents in comparison with a peak of value 600 with another histogram.
I looked at the source code of the function spec.pgram to better understand what is behind. But, when I apply the source code line by line, I've got a problem. For instance, I make:
>data = scan ("file.txt")
>h = hist (data, breaks=max(data)/5000)
#then I apply the first two lines of the spec.pgram function
>series <- deparse(substitute(h$counts))
>x <- na.action(as.ts(h$counts))
>x

NULL
I do not understand why when I apply the first two lines of the function I have x which is equal to NULL (which make a mistake in the following lines of the code) but if I apply the function directly with h$counts it gives me a result.
So, if someone can explain to me what is the problem and/or how spec.pgram exactly computes the periodogram and how to interpret it with my data, I would be so grateful.
And subsidiary questions:
- Is it possible to have the commented source code of the function? - I do not understand what is the function na.action in the second line of spec.pgram, so if you can explain it to me.

Thanks in advance for your answers.
Best regards,

Anthony Mathelier

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