there are some inconsistencies between the behavior of tables and that of flow variables. One well-known one is that a table can contain missing values but a flow variable cannot; the Table Row To Variable and Table Row To Variable Loop Start force the user to replace the missing value with a non-missing default value, to fail the execution, or to omit the variable entirely. I guess that the reason behind this is that, for example, the Java Double class does not support missing values and making a special DoubleKNIME class would not be worth the added complexity. Similarly, allowing the variable to be “null” would probably lead to a software engineering nightmare.
Another inconsistency is that when evaluating 0/0 in a Math Formula node, the result is a missing value. In the Math Formula (Variable) node, the result is NaN. When this is converted to a table with a Variable to Table Column node, the result is a column filled with NaNs. I.e., the result of identical expressions is different depending on whether they are performed on variables or tables.
Here is another inconsistency that I came across today. Suppose I have a table:
and I want to convert it to integers using the Math Formula node:
The result is exactly what I would expect, a table where original column has been replaced:
Let’s try this with a flow variable:
and a Math Formula (Variable) node:
The result is TWO flow variables with the same name but different types, even though “Replace” is checked.
I think the “Replace Variable” option should be greyed out when the “Convert to Int” option is checked.