[R] Fourier Transform with irregularly spaced x

[Claudia Beleites]

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