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

[Jim Lemon]

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