[R] Finding First of a Type in a Sequence

[David Winsemius]

On Apr 26, 2010, at 12:29 PM, Su Chu wrote:

> Hi there,
>
> I am working on a project that requires me to find the point at  
> which values
> become negative in a sequence about the max.
>
> For example, say I have some sequence:
>
> x=c(-12, -2,-19, 0, -14, -2, 9,10,20,35,56,89,60,39,12,8,-5,-2,0,10)

 > x[ c( which.max(x) -min(which(x[which.max(x):1] < 0)) +1,
+ which.max(x) +min(which(x[which.max(x):length(x)] < 0)) -1) ]
[1] -2 -5

>
> In this sequence, the max is 89, and I need to identify that -2 and  
> -5 are
> the points at which the values* first *become negative about the max  
> and
> retrieve their index values.
>
> I was hoping for some help in finding a way to automate this  
> procedure, as I
> have over 100 vectors of this kind where I must find the two values  
> about
> the max.
>
> Could anyone help? I would really, really appreciate it!
>
>
> Thank you so much!
>
> Best,
> Su
>
> 	[[alternative HTML version deleted]]
>
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David Winsemius, MD
West Hartford, CT