[R] Stuck with FFT
seb.brockel at northampton.ac.uk
Tue Oct 28 11:04:41 CET 2008
EDIT: to assist you to assist me in turn, for which I am grateful, more
detail than the below needs to be provided.
I open tables and view them using Rcmdr so they become active datasets. I am
assuming that x101, x100, etc, are column headings because when the dataset
is edited they can be changed in numerical or non-numerical values. Lets
assume I change those column headings to VB! and V2, and I would like the
output to appear in V3. V2 contains the values to be fft'd. These are
practise values of 24h length sinusoids thus if a sinusoid is viewed as a
frequency value and the time-series are hourly values where periodicity, not
amplitude, counts, this is a 24hr frequency time-series fo hourly values.
Here's an example table (to keep it simple, there are 2 columns, V1 for the
24h frequency values, and V2 for fft output, I don not understand the fft
function enough yet if V1 should contain date/ time values and if V2 should
contain the array, and V3 the output values);
The table name, I assume, since it appears in the window border and taskbar,
This is open as a table by view command. How do I go about fft'ing this?
If I can do this I can then in turn try to analyse my real radon data which
are hourly time-series (thus is a disctrete and periodic array). I have to
analyse it for periodicities that can be attributed to 24hr and 24.8hr tidal
cycles to confirm the substance of the first aim of my research.
Secondly, how can I view the output as a graph? I am expecting a frequency
domain from the time domain, thus a frequency of a certain amplitude should
Thank you very much. I hope this clears the matter up a bit. If not, I am
happy to provide more details.
> Dear all,
> Before I can get into serious Fourier analysis of Radon time-series I am
> practising with 24hour and 24.8hour sinusoids to assist with my
> interpretation of signals ittributed to tidal input to Radon time series.
> I am stuck. I have tried researching this to no avail. I am awating a book
> that should describe fourier transforms in detail and another one that
> should discuss the R application.
> I know what the command line is but I can't get it to refer to the array.
> What is 'z'? If I have a table open entitled '24hsinusoids' with date/
> time column by the hour from January 01 2008 00:00 to January 02 2011
> 00:00 (X01.06.2008) (time column listed as X00:00) with corresponding
> sinudoidal signal value column (X100) to give a complete curve for 24hours
> spread as curves over the whole time-span, how can I fft from this table?
> fft(z, inverse = FALSE) gives me as; object 'z' not found.
> Please help and explain how R recognises the table and does fft's from it.
> The time-series is discrete and periodic (or should be, as I need to
> analyse my Radon time-series fro exactly this and I am very stuck now).
> Thank you with all my heart if you can help.
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