Retrieve values of local maxima in R data table - already have column numbers

Question

using this question's solution: Finding local maxima and minima I have been able to retrieve what seems to be a list of column numbers from my data table for local maxima. I also need to retrieve the value of that peak from the table. Preferably I would return a matrix or equivalent where each row contains the local peak values rather than the positions, as I already have the positions

so say using a vector ex_data <-c(1,3,2,2,1,3,5,4,2,1) I would want to get a vector saying (3,5). I already have the code below:

local_max <- function(x) {
which(diff(sign(diff(x)))==-2)+1}
local_max(ex_data)

which produces vector (2,7)

Hi there! Please make your post reproducible. Read the post [**how to make a great reproducible example**](http://stackoverflow.com/questions/5963269/how-to-make-a-great-r-reproducible-example) on how to do this. Thank you. — Arun, Mar 20 '13 at 13:40

score 0 · Accepted Answer · answered Mar 20 '13 at 13:57

0

It's easy. Just use the index vector for subsetting.

ex_data[local_max(ex_data)]

answered Mar 20 '13 at 13:57

Sven Hohenstein

80,497
17
145
168

So simple, thank you! I've done this type of thing in python a hundred times but R is a mystery to me at the moment! – bioinformagician Mar 20 '13 at 14:00

Retrieve values of local maxima in R data table - already have column numbers

1 Answers1