R help - Jan 2009 - Plot, lines and disordered x and y

Hello,

I have 2d data where x coordinate is not given in usual ascending
order (x1,...,x1+l; l>0), and instead in another, regular, but not
ascending or descending order (for illustration:
x1,-x1,x1+dx1,-x1-dx1,....).y is an array which corresponds to the way
x is ordered. I have noticed that giving 'plot(x,y,type='l')
produces
a plot where the points are connected in a completely wrong way. It is
as the plot/lines assumes an ascending order between the succesive y
points ignoring the fact that they are not (it connects y(x1) with
y(-x1), for x1+dx). I don't know whether this could be a bug, because
maybe sorting the y coordinates appropriately and then interpolating
lines plotting is too much to ask of the plot function. But, I've felt
like sharing :-)

Additionally, 'points' function will plot the data properly.

Cheers,

TK

Ok, here is a bit more information:

R is version 2.7.1 (2008-06-23)

A constructed example:
....
> x<-c(1,-1,2,-2,3,-3,4,-4,5,-5)
> y<-c(1,0,2,0,3,0,4,0,5,0)
> plot(x,y,type='l')   #bad
> plot(x,y) # this is how it should look like
....

So what we should see here is a flat y=0 for x<0 and identity for x>0.
Instead, we have a saw-like shape where e.g y(x=-1) is connected to
y(x=1) .

This is of course minor  (actually asymptotically, no annoyance at
all). I am just mentioning it for 'completness' sake and because a
divinely ideal plotting function should cope with data given in any
order.

Cheers!

TK

Cheers,

TK



2009/1/23 jim holtman <jholtman at gmail.com>:
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>
> A sample of data causing the problem would help.  It is most likely
> the way you have it specified.
>
> On Fri, Jan 23, 2009 at 11:37 AM, Todor Kondic <dolichenus at
gmail.com> wrote:
>> Hello,
>>
>> I have 2d data where x coordinate is not given in usual ascending
>> order (x1,...,x1+l; l>0), and instead in another, regular, but not
>> ascending or descending order (for illustration:
>> x1,-x1,x1+dx1,-x1-dx1,....).y is an array which corresponds to the way
>> x is ordered. I have noticed that giving
'plot(x,y,type='l') produces
>> a plot where the points are connected in a completely wrong way. It is
>> as the plot/lines assumes an ascending order between the succesive y
>> points ignoring the fact that they are not (it connects y(x1) with
>> y(-x1), for x1+dx). I don't know whether this could be a bug,
because
>> maybe sorting the y coordinates appropriately and then interpolating
>> lines plotting is too much to ask of the plot function. But, I've
felt
>> like sharing :-)
>>
>> Additionally, 'points' function will plot the data properly.
>>
>> Cheers,
>>
>> TK
>>
>> ______________________________________________
>> 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.
>>
>
>
>
> --
> Jim Holtman
> Cincinnati, OH
> +1 513 646 9390
>
> What is the problem that you are trying to solve?
>

Todor Kondic <dolichenus <at> gmail.com> writes:

 > This is of course minor (actually asymptotically, no annoyance at
 > all). I am just mentioning it for 'completness' sake and because a
 > divinely ideal plotting function should cope with data given in any
 > order.
 >

It's not just a question of 'how many divine orders' there are, as 
others have pointed out.

The fact is:  if you define a vector, you have defined the order of the 
components in the vector.  if

x<-c(1,-1,2,-2,....)  then x[1] is 1 and x[2] is 2.

That is the way every software program, and every statistician, 
mathematician, and scientist agrees to define vectors.

If you want your data to be in a different order, there is no magical 
'mind-reading' tool that can order it the way you are thinking of.  You 
have to load values into your vectors (or matrices, or whatever) in the 
proper established order.

I can understand your frustration, because we've all seen datasets where 
it would be useful and/or instructive to plot a visually-obvious subset 
of the data.  It just takes a little work on each of our part to 
re-order, or sort, or extract, the points of interest into new vectors.

Carl