How to create a column with a quartile rank?

A data.table approach

    library(data.table)
    tableOne <- setDT(tableOne)[, quartile := cut(salesPrice, quantile(salesPrice, probs=0:4/4), include.lowest=TRUE, labels=FALSE)]

This should do it:

tableOne <- within(tableOne, quartile <- as.integer(cut(salesPrice, quantile(salesPrice, probs=0:4/4), include.lowest=TRUE)))

...Some details:

The within function is great for calculating new columns. You don't have to refer to columns as tableOne$salesPrice etc.

tableOne <- within(tableOne, quartile <- <<<some expression>>>)

The quantile function calculates the quantiles (or in your case, quartiles). 0:4/4 evaluates to c(0, 0.25, 0.50, 0.75, 1).

Finally the cut function splits your data into those quartiles. But you get a factor with weird names, so as.integer turns it into groups 1,2,3,4.

Try ?within etc to learn more about the functions mentioned here...