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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