Sometimes the data that you have requires further processing; that is, not just moving around but also changing some values.
A quite flexible node is the Rule Engine node that creates or replaces a column based on certain rules involving other columns. It might contain logical and relational operators for texts, and it can even check for inclusion (IN) for a certain set of values or limited pattern matching (LIKE as in SQL). The result can be either a constant, a column's value, or a flow variable. It can also handle the missing values.
When you want to fill the metadata, you should use the Domain Calculator node. With the help of this node, you can create nominal columns from textual (String) columns.