cor shows only NA or 1 for correlations - Why?

Question

I\'m running cor() on a data.framewith all numeric values and I\'m getting this as the result:

       price exprice...
price      1         


        

Answer 1

NAs also appear if there are attributes with zero variance (with all elements equal); see for instance:

cor(cbind(a=runif(10),b=rep(1,10)))

which returns:

   a  b
a  1 NA
b NA  1
Warning message:
In cor(cbind(a = runif(10), b = rep(1, 10))) :
  the standard deviation is zero