7  Select

7.1 Select columns with data.table

7.1.1 Example

To select columns age, sex, and smoking, you can use the following:

7.1.2 Practice

Your turn: Complete the following code to select columns “platelets”, “serum_creatinine”, and “serum_sodium”:

Explanation

Solution:

hf_pss <- hf[, .(platelets, serum_creatinine, serum_sodium)]
# also
hf_pss <- hf[, list(platelets, serum_creatinine, serum_sodium)]

In data.table, we refer to column names directly without using quotes. To select columns, we use the j argument of the data.table syntax, which is a list of column names to select. In data.table, the .() notation is a shorthand for list().

For more information, see ?data.table::\\[.data.table`.