[R] How to label certain values on a curve?

[(Ted Harding)]

On the subject of identify() [perhaps I should change thread]:

'?identify' clearly states:

  Value:
    If 'pos' is 'FALSE', an integer vector containing the indices
    of the identified points, in the order they were identified.

However, I find that the result is not in the order of identification,
but rather with the indices sorted in increasing order. Example:

  set.seed(54321); x<-rnorm(100); y<-rnorm(100)
  plot(x,y)

Now go anticlockwise round the points which you judge to be
the vertices of the convex hull of this plot, using

  ix <- identify(x,y,plot=FALSE,pos=FALSE)

I see 9 such points, and I start with the one with smallest y value,
going anticlockwise. The result is

  ix
  # [1]  8 15 17 21 25 44 63 94 99

and now:

  lines(x[ix],y[ix])

while it joins the points, does not do so in the order in which they
were identified. Using

  identify(x,y,plot=TRUE,pos=FALSE)

puts the indices as labels on the points, and the order of
identification (read off anticlockwise from the graph) is:

  25 21 17  8 44 99 63 15 94

This is on R version 2.11.0 (2010-04-22), Debian Linux, X11.
Have things changed since then?

Ted.


On 06-Jun-2012 16:38:14 R. Michael Weylandt wrote:
> Take a look at the identify() function.
> 
> Best,
> Michael
> 
> On Wed, Jun 6, 2012 at 11:23 AM, Wendy Han <wendyhan08 at gmail.com> wrote:
>> Hi all,
>>
>> I have drawn a curve in R and observed some interesting values, I wonder if
>> there is any method to mark certain values on this curve, so that I
>> can manually choose the point and know the exact value of this point
>> simultaneously? I appreciate your suggestions and advice!
>>
>> Thanks a lot!
>> Wendy

-------------------------------------------------
E-Mail: (Ted Harding) <Ted.Harding at wlandres.net>
Date: 06-Jun-2012  Time: 22:25:14
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