[R] Cannot rescale a constant/zero column error.

[PIKAL Petr]

Hi

> 
> Jim,
> 
> Thank you for your reply.  I guess I am just not understanding what the
> difference is.  If I run your example using the pcmatrix<-
> data.frame(Q1=sample(1:5,10,TRUE),Q2=sample(1:5,10,TRUE)) and print out
> pcmatrix I get:
> 
> 	Q1	Q2
> 1	98	99

Thats rather surprising. I get

> pcmatrix<-data.frame(Q1=sample(1:5,10,TRUE),Q2=sample(1:5,10,TRUE))
> pcmatrix
   Q1 Q2
1   4  4
2   3  3
3   4  1
4   4  4
5   4  2
6....

this what I get


> 
> Then if I mirror my input file to be, would would be what the samples
> from above would have created, it would look like this:
> 
> ID,Q1,Q2
> 1,2,3

what about include 

dput(head(yourfile)) 
to your post to let us see how it looks like. Or at least 

str(yourfile)

Regards
Petr


> 
> And I run the script printing out pcmatrix I get the exact same thing.
> 
> 	Q1	Q2
> 1	98	99
> 
> So I would think they are basically the same representations, however
> one works when passed into the prcomp function and the other does not.
> I am just trying to tweak a script that we had created for us (cannot
> find the guy now) so I can pass more columns of data.  I clearly really
> do not know what I am doing, but again thanks for you time and any
> direction you can point me in would be awesome.
> 
> Thanks
> 
> Jason
> 
> On Nov 1, 2012, at 3:57 AM, Jim Lemon wrote:
> 
> > On 10/31/2012 11:47 PM, fillay89 wrote:
> >> I am trying to run the R Script below, I have actually simplified it
> >> to just this part that is causing issues.  When I run this script I
> >> continue to get an error that says "cannot rescale a constant/zero
> >> column to a unit variance".  I cannot figure out what is going on
> >> here.  I have stripped down my data file so it is more manageable so
> I can try to figure this out.
> >>
> >> The data.txt file that is being read looks like this:
> >>
> >>
> >> I have made this file very basic on purpose to see if I could get
> >> this to work, but it is not working.  Of course once I get this to
> >> actually work I will expand the data file to match the data I am
> actually using.
> >>
> >>
> >>
> >> If I change the attribute in the prcomp function to scale=FALSE of
> >> course I can run my script.  But if it is scaling...which is causing
> >> the issues, it errors.
> >>
> >> Any help would be GREATLY appreciated.
> >>
> > Hi fillay89,
> > You seem to be trying to run a principal component analysis on two
> numbers, which won't produce anything useful. If I make up some data
> that is more realistic:
> >
> > pcmatrix<-data.frame(Q1=sample(1:5,10,TRUE),Q2=sample(1:5,10,TRUE))
> > pcmatrix[,1] <- pcmatrix[,1] + 96
> > pcmatrix[,2] <- pcmatrix[,2] + 96
> > x.pca <- prcomp(pcmatrix,retx=TRUE,center=TRUE,scale=TRUE,cor=TRUE)
> > x.pca
> > Standard deviations:
> > [1] 1.263267 0.635733
> >
> > Rotation:
> >         PC1        PC2
> > Q1 0.7071068 -0.7071068
> > Q2 0.7071068  0.7071068
> >
> > it runs and I get a slightly more useful result. Running your code
> does bomb in exactly the way you describe, as does:
> >
> > x.pca <- prcomp(data.frame(Q1=99,Q2=98), retx=TRUE, center=TRUE,
> > scale=TRUE, cor=TRUE) Error in prcomp.default(data.frame(Q1 = 99, Q2
> = 98), retx = TRUE, center = TRUE,  :
> >  cannot rescale a constant/zero column to unit variance
> >
> > Your problem is that you have a data frame with only one value (i.e.
> a constant) in each column.
> >
> > Jim
> 
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