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13 messages · Chen Huashan, Friedrich Leisch, dechao wang +3 more

Chen Huashan
# 
Dear R help users:

I have set up a r help mailing list archive based on mysql which support
full text search and auto-update.

Please visit http://www.baidao.net/r/maillist/index.cgi  . I hope you could 
provide me bug reports and suggestions. 

I will add r_dev and r_announce mailing list as soon as possible.

Thanks in advance!


eLan 
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Friedrich Leisch
# 
> Dear R help users:
  > I have set up a r help mailing list archive based on mysql which support
  > full text search and auto-update.

  > Please visit http://www.baidao.net/r/maillist/index.cgi  . I hope you could 
  > provide me bug reports and suggestions. 

  > I will add r_dev and r_announce mailing list as soon as possible.

  > Thanks in advance!


Wow, this looks great. I'll put links to it on CRAN once you have
support for the other two lists, too. Please let me know when you're
ready.

Thanks a lot for this effort!

All the best,
Fritz
dechao wang
# 
Hi, I have checked statistic textbooks about
correlations, but I am still not sure the correlation
analysis with different units, for example,

x1<-c(1,  2,  3,   100, 200, 300)
x2<-c(1.1,2.8,3.3, 108, 209, 303)
the unit of the first 3 numbers is cm
the unit of the last 3 numbers is kg

cor(x1,x2)=0.999655

Can I explain the correlation coefficient as normal in
which all numbers have the same unit?

Secondly, if keep the three large numbers unchanged,
just change the three small numbers, the coefficient
changes little, this means that the variation of three
small numbers is hidden by the three larger numbers.
Is there any solution in R to solve this issue?

Thanks,

Dechao

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Laurent Gautier
# 
Dear Chen,


  I just tried it too.

It looks really really helpful (the highlighted query words in the
body of the mail is nice) ! Thanks !

  Is there a plan to include older archives (I tried the time constraint 
'all posts' but it seems that it does not go to far in the past) ?




  Regards,



  Laurent




Laurent Gautier			CBS, Building 208, DTU
PhD. Student			D-2800 Lyngby,Denmark	
tel: +45 45 25 24 85		http://www.cbs.dtu.dk/laurent
On Thu, 7 Mar 2002 Friedrich.Leisch at ci.tuwien.ac.at wrote:

            

      
      
      
    

        
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      Chen Huashan
    

    

      
      #
    

  


  

      
Hi Laurent,

The archive currently contains messages from 20002-2.
I will try to add all messages of three lists as soon as possible.

btw: how about the server's transfer rate?

Best wishes

Chen

            

      
      
      
    

        
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      Joerg Maeder
    

    

      
      #
    

  


  

      
Hello

        
dechao wang wrote:

            

      
      
      
    

        
No, that will give different results. The unit must be the same for all
values. Which unit isn't important, but it must be the same

            

      
      
      
    

        
If you have a vector with the units, you can use it to bring all values
to the same unit

eg (for two different units, if there are more it will be more
complicated)
xu <- c('m','m','m','cm','cm','cm') #units
cor(ifelse(xu=='m',100,1)*x1,ifelse(xu=='m',100,1)*x2)

gruess

joerg

        

      
      
    

        

  
    

      
      
    

  


  


      

    

    

      
      

        


  

        

      Andrew Perrin
    

    

      
      #
    

  


  

      
On Thu, 7 Mar 2002, [iso-8859-1] dechao wang wrote:

        

            

      
      
      
    

        
I don't think the correlation depends on the units; it's a ratio, not an
absolute. Consider the case of making the centimeters into meters:

            

      
      
      
    

        
[1] 0.999655

The correlation doesn't change.

            

      
      
      
    

        
I'm not sure what you mean by "hidden"; in your case, the correlations
between the vectors are similar for both first and second halves:

            

      
      
      
    

        
[1] 0.9997853

            

      
      
      
    

        
[1] 0.953821

so removing either half isn't going to change the result much.


----------------------------------------------------------------------
Andrew J Perrin - andrew_perrin at unc.edu - http://www.unc.edu/~aperrin
 Assistant Professor of Sociology, U of North Carolina, Chapel Hill
      269 Hamilton Hall, CB#3210, Chapel Hill, NC 27599-3210 USA




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      Andrew Perrin
    

    

      
      #
    

  


  

      
On Thu, 7 Mar 2002, Joerg Maeder wrote:

        

            

      
      
      
    

        
OOPS - I apologize, I misread the question, I understood the OP to be
saying that x1 was in cm and x2 was in kg. 

What on earth would a correlation mean between two vectors, each of which
is made up of two entirely different measures? (These aren't just
different units, they're measures of entirely different phenomena.)


----------------------------------------------------------------------
Andrew J Perrin - andrew_perrin at unc.edu - http://www.unc.edu/~aperrin
 Assistant Professor of Sociology, U of North Carolina, Chapel Hill
      269 Hamilton Hall, CB#3210, Chapel Hill, NC 27599-3210 USA




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      dechao wang
    

    

      
      #
    

  


  

      
Thanks Andrew,

Consider the following example:

            

      
      
      
    

        
[1] 0.999655

            

      
      
      
    

        
[1] 0.9997286

You can see that as x2 changed to x3 with only first
three numbers changing, the coefficients (x1, x2) and
(x1,x3) changed little. I thought this may be because
the last three numbers were in different units.

Consider another example:

            

      
      
      
    

        
[1] 0.9934715

            

      
      
      
    

        
[1] 0.9254707

You can see that the coefficients (y1,y2) and (y1,y3)
are different as the first three numbers changed.

            

      
      
      
    

        
of compatibility bewteen items that contain different
units is lower (as shown in the first example) than
that of compatibility of items that contain the same
scale (as shown in example 2).

The results of the first example is not what we want,
isn't it? So I think it would be better if pre-process
the data that contain different units before
regression analysis. I do not think it is difficult to
write code using R to do that. My question is there
command already exist to do that before I write code?




 --- Andrew Perrin <andrew_perrin at unc.edu> wrote: > On

        
Thu, 7 Mar 2002, [iso-8859-1] dechao wang wrote:

            

      
      
      
    

        
----------------------------------------------------------------------

            

      
      
      
    

        
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      Andrew Perrin
    

    

      
      #
    

  


  

      
On Thu, 7 Mar 2002, [iso-8859-1] dechao wang wrote:

        

            

      
      
      
    

        
It's not because they're different units -- it's because they're different
measures altogether! Can you state, in words (e.g., not in mathematical
terms) what you think a correlation would *mean* between these two
vectors?  R is happily telling you, as any statistical package would, what
the correlation is between two vectors of numbers. But that correlation
doesn't necessarily mean anything at all; its meaning is based on what the
vectors measure.

----------------------------------------------------------------------
Andrew J Perrin - andrew_perrin at unc.edu - http://www.unc.edu/~aperrin
 Assistant Professor of Sociology, U of North Carolina, Chapel Hill
      269 Hamilton Hall, CB#3210, Chapel Hill, NC 27599-3210 USA




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      dechao wang
    

    

      
      #
    

  


  

      
--- Andrew Perrin <andrew_perrin at unc.edu> wrote: > On

        
Thu, 7 Mar 2002, [iso-8859-1] dechao wang wrote:

            

      
      
      
    

        
There are lots of examples. Let us consider the first
three numbers representing three branches of an apple
tree, the last three numbers representing the
corresponding branching angles of the branches. So x1,
x2, x3 represents three different trees. Maybe we can
ask which tree is similar to which tree?

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      Andrew Perrin
    

    

      
      #
    

  


  

      
On Thu, 7 Mar 2002, [iso-8859-1] dechao wang wrote:

        

            

      
      
      
    

        
as any

            

      
      
      
    

        
In which case you probably shouldn't be storing the data in vectors
(although you can), but you certainly shouldn't be using correlations to
measure similarity among vectors where each vector represents one unit of
analysis.  There are various ways of classifying the "similarity" among
vectors (indeed, Brian Ripley of Venables and Ripley fame is an expert in
this field) but correlation is not one of them.

You could ask, in your example, whether the length of a branch is
correlated with its angle; in that case, you'd want something like:
x1<-c(1,  2,  3,   100, 200, 300)
x2<-c(1.1,2.8,3.3, 108, 209, 303)
x3<-c(2.8,3.8,5.3, 108, 209, 303)
x.df<-as.data.frame(t(data.frame(x1,x2,x3)))
colnames(x.df)<-c('l1','l2','l3','a1','a2','a3')attach(x.df)
cor(l1,a1)

which returns:
[1] 0.5421936

or the correlation between length 1 (l1) and angle 1 (a1). That's a
suitable (although not very sophisticated) use of correlation. But
measuring the correlation between cases using different measures is not a
useful, or even meaningful, exercise, IMNSHO.


----------------------------------------------------------------------
Andrew J Perrin - andrew_perrin at unc.edu - http://www.unc.edu/~aperrin
 Assistant Professor of Sociology, U of North Carolina, Chapel Hill
      269 Hamilton Hall, CB#3210, Chapel Hill, NC 27599-3210 USA




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2 days later

    

      
      

        


  

        

      Chen Huashan
    

    

      
      #
    

  


  

      
Dear R help users:

All the posts of r-help list before 2001-12-28 have been added to database!
The address is : http://www.baidao.net/r/maillist/archive/index.cgi

The old address (http://www.baidao.net/r/maillist/index.cgi ) is still under testing

The other two lists will be added untile r-help list archive is considered stable enough.

All the bests!

Chen Huashan

            

      
      
      
    

        
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