Numeric data is not numeric.

General
2

You can use the str function to find out what type a variable is.

For example

df <- data.frame(c1 = 1:3, c2 = c(1.2, 1.3, 1.4), c4 = LETTERS[1:3])
str(df)
#> 'data.frame':    3 obs. of  3 variables:
#>  $ c1: int  1 2 3
#>  $ c2: num  1.2 1.3 1.4
#>  $ c4: Factor w/ 3 levels "A","B","C": 1 2 3

Created on 2019-05-08 by the reprex package (v0.2.1)

Note this tells you that c1 and c2 are both numerics (an integer and a floating point are both considered numerics by R), where c4 is a factor.

As a note, it is extremely hard to help debug code and/or error messages when screenshots are posted. Posting screenshots, instead of actual code/error messages, is likely to decrease your chances of getting the help you are looking for in general.

I'd encourage you to ask this kind of question with a minimal REPRoducible EXample (reprex)? A reprex makes it much easier for others to understand your issue and figure out how to help.