r - Finding local maxima and minima -

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i'm looking computationally efficient way find local maxima/minima large list of numbers in r. without for loops...

for example, if have datafile 1 2 3 2 1 1 2 1, want function return 3 , 7, positions of local maxima.

diff(diff(x)) (or diff(x,differences=2): @zheyuanli) computes discrete analogue of second derivative, should negative @ local maxima. +1 below takes care of fact result of diff shorter input vector.

edit: added @tommy's correction cases delta-x not 1...

tt <- c(1,2,3,2,1, 1, 2, 1) which(diff(sign(diff(tt)))==-2)+1

my suggestion above ( http://finzi.psych.upenn.edu/r/library/ppc/html/ppc.peaks.html ) intended case data noisier.


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