R help - Apr 2010 - Finding First of a Type in a Sequence

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)

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]]

Try this:



func <- function(x)
{
which.negative <- which(x<0)
index.to.return <- which.negative[which.negative > which.max(x)][1]
return(index.to.return)
}

func(x)


Best,
Tal

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On Mon, Apr 26, 2010 at 7:29 PM, Su Chu <sushikyc@gmail.com> 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)
>
> 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]]
>
> ______________________________________________
> R-help@r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>
	[[alternative HTML version deleted]]

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]]
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
David Winsemius, MD
West Hartford, CT