Question

___ is used to extract elements of a list or data frame by name, and the class of the returned object will not necessarily be a list or data frame.

A. $.
B. [].
C. [[.
D. None of the above.

Answer 1

The correct answer is [[.

Step-by-step explanation:

The correct answer to this question is [[. The [[ operator is used to extract elements of a list or data frame by name. The returned object will not necessarily be a list or data frame because it depends on the specific element being extracted. For example, if the specified element is a single value, the returned object will be of that value's class.