[R] Fourier Transform with irregularly spaced x

[stephen sefick]

You need to decide how you are going to interpolate the values.  Look
at the zoo package- na.approx() .   spectrum() take the x axis and
produces a power spectrum vs. cycles/time.  you may interpret this
however it makes ssnse- if it makes sense.

On Mon, Nov 3, 2008 at 4:23 AM, Claudia Beleites <cbeleites at units.it> wrote:
> Dear all,
>
> I work with (vibrational) spectra: some kind of intensity (I) over frequency
> (nu), wavelength or the like.
> I want to do fourier transform for interpolation, smoothing, etc.
>
> My problem is that the spectra are often irregularly spaced in nu: the
> difference between 2 neighbouring nu varies across the spectrum, and data
> points may be missing.
>
> Searching for discrete fourier transform I found lots of information and
> functions - but I didn't see anything that just works with irregularly spaced
> signals: all functions I found take only the signal, not its x-axis.
>
> Where should I look?
> Or am I lacking some math that tells how to do without the frequency axis?
>
> Thanks a lot for your help,
>
> Claudia
>
>
> --
> Claudia Beleites
> Dipartimento dei Materiali e delle Risorse Naturali
> Università degli Studi di Trieste
> Via Alfonso Valerio 6/a
> I-34127 Trieste
>
> phone: +39 (0 40) 5 58-34 47
> email: cbeleites at units.it
>
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-- 
Stephen Sefick
Research Scientist
Southeastern Natural Sciences Academy

Let's not spend our time and resources thinking about things that are
so little or so large that all they really do for us is puff us up and
make us feel like gods.  We are mammals, and have not exhausted the
annoying little problems of being mammals.

								-K. Mullis