6  Filter

6.1 Introduction

Filtering a dataset is the process of indexing a subset of the cases, i.e. rows.

6.2 Filter rows with data.table

6.2.1 Example

To filter the hf dataset to only include rows where age is greater than 60, we can use the following code:

6.2.2 Practice

Your turn: Complete the following code to filter all cases with serum_creatinine greater than 1.4:

Now, use the custom function check() to check your answer:

Explanation

Solution:

hf_high_creat <- hf[serum_creatinine > 1.4]

In data.table, we refer to column names directly without using quotes. In contrast to data.frames, we don’t need to include a comma after filtering rows in the i argument, but it would work just the same if we did, for example:

hf_high_creat <- hf[serum_creatinine > 1.4, ]

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