[R] Variogram with time series

[consentino@infinito.it]

Hello,
  
I'm using a dataset with unequally spaced time series
and I'd want to know if there is in R some functions in
order to calculate the autocorrelation function, because
acf() in stats package cannot calculate it, because I
have many missing data.
  
And if so, is it necessary to organize dataset in ts
structure or is it possible to consider it like a simple
vector?
  
Thanks in advance
  
Fabrizio Consentino
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