NA
NA
NA in DataFrame can be seen as "NaN or null".
Floats or Doubles can be represented as Float.NaN or Double.NaN, respectively, in cases where a mathematical operation is undefined, such as dividing by zero.
A DataRow can also be considered NA if each value inside is NA.
A DataFrame is considered NA if it has no rows or columns, so if it's empty.
You can also use fillNA to replace NAs in certain columns with a given value or expression or dropNA to drop rows with NAs in them.
For more information: See NA on the documentation website.