Correlation with discrete and categoric variables in R

Question

I am analyzing this dataset it has numeric and factor variable. I would like to know the correlation so I can choose the best variables.

str(data)
$ Ag                    : num [1:1470] 41 49 37 33 27 32 59 30 38 36 ...
 $ Ay              : Factor w/ 2 levels "No","Yes": 2 1 2 1 1 1 1 1 1 1 ...
 $ Bu        : Factor w/ 3 levels "Non-Travel","Travel_Frequently",..: 3 2 3 2 3 2 3 3 2 3 ...
 $ Di       : num [1:1470] 1 8 2 3 2 2 3 24 23 27 ...
 $ Ed               : num [1:1470] 2 1 2 4 1 2 3 1 3 3 ...
 $ Ep          : num [1:1470] 1 1 1 1 1 1 1 1 1 1 ...
 $ Em          : num [1:1470] 1 2 4 5 7 8 10 11 12 13 ...
 $ Ge                : Factor w/ 2 levels "Female","Male": 1 2 2 1 2 2 1 2 2 2 ...
 $ Ho             : num [1:1470] 94 61 92 56 40 79 81 67 44 94 ...
 $ J1         : num [1:1470] 3 2 2 3 3 3 4 3 2 3 ...
 $ J2               : num [1:1470] 2 2 1 1 1 1 1 1 3 2 ...

When I execute this(althought I want correlations of all data not only numeric):

cor(data[sapply(data, is.numeric)])

I return this message:

Warning message:
In cor(data[sapply(data, is.numeric)]) :
  the standard deviation is zero

Answer 1

It just politely lets you know that you set out to calculate correlation where one of the variables is constant. This often pointless.

Just filter that out aswell

x1 <- data[sapply(data,is.numeric)]
x2 <- x1[sapply(x1,sd)!=0]

cor(x2)