[R] Stuck with FFT
seb.brockel at northampton.ac.uk
Thu Oct 30 14:58:05 CET 2008
Well, I would like to thank you all for your assisstance.
I am now progressing and detecting tidal signals in my radon time series.
I really appreciate this.
I am not stuck with research now.
> 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, is 'Dataset'.
> V1 V2
> 1 105
> 2 115
> 3 140
> 4 180
> 5 230
> 6 300
> 7 360
> 8 418
> 9 450
> 10 480
> 11 495
> 12 500
> 13 495
> 14 480
> 15 450
> 16 410
> 17 360
> 18 300
> 19 230
> 20 180
> 21 140
> 22 115
> 23 105
> 24 100
> 25 105
> 26 115
> 27 140
> 28 180
> 29 230
> 30 300
> 31 360
> 32 410
> 33 450
> 34 480
> 35 495
> 36 500
> 37 495
> 38 480
> 39 450
> 40 410
> 41 360
> 42 300
> 43 230
> 44 180
> 45 140
> 46 115
> 47 105
> 48 100
> 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
> 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 be produced.
> Thank you very much. I hope this clears the matter up a bit. If not, I am
> happy to provide more details.
> Rthoughts wrote:
>> 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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