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The data.frame() function has an optional argument stringsAsFactors, which prevents the character columns' automatic conversion into factors. A factor is another R data type that is used to represent categorical variables such as 1 for M and 2 for the F category. In the dataset that you have created using the data.frame() function, notice that the column GENDER is a factor type, though you did not explicitly mention it. Intuitively, the GENDER column should be a character column with values M and F. To prevent this automatic conversion, you must use stringsAsFactors=FALSE as follows:

    datB <- data.frame(ID = 1:5, hourSpetOnInternet = c(5,3,4,1,2),  
    GENDER = c("M", "F", "F", "M", "F"), stringsAsFactors=FALSE)