Finding lag at which cross correlation is maximum ccf( )

Question

I have 2 time series and I am using ccf to find the cross correlation between them. ccf(ts1, ts2) lists the cross-correlations for all time lags. H

Answer 1

Because 3 is more than 4, I also had a stab at modifying this function, this time by implementing an idea from here:

ccfmax <- function(a, b, e=0)
{
 d <- ccf(a, b, plot = FALSE, lag.max = length(a)/2)
 cor = d$acf[,,1]
 abscor = abs(d$acf[,,1])
 lag = d$lag[,,1]
 res = data.frame(cor, lag)
 absres = data.frame(abscor, lag)
 maxcor = max(absres$abscor)
 absres_max = res[which(absres$abscor >= maxcor-maxcor*e &
                        absres$abscor <= maxcor+maxcor*e),]
 return(absres_max)
}

Essentially an "error" term is added, so that if there are several values close to the maximum, they all get returned, eg:

ayy <- jitter(cos((1:360)/5), 100)
bee <- jitter(sin((1:360)/5), 100)

ccfmax(ayy, bee, 0.02)
           cor lag
348  0.9778319  -8
349  0.9670333  -7
363 -0.9650827   7
364 -0.9763180   8

If no value for e is given it is taken to be zero, and the function behaves just like the one nvogen posted.