Signature Description
enum class drop_policy : unsigned charĀ  {
 all = 1, // Remove row if all columns are nan
 any = 2, // Remove row if any column is nan
 threshold = 3 // Remove row if threshold number of columns are nan
};
This policy specifies what rows to drop/remove based on missing column data
all: Drop the row if all columns are missing
any: Drop the row if any column is missing
threshold: Drop the column if threshold number of columns are missing