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Saturday, 15 September 2012

Selecting attribute subsets using macros: a minor foible and workaround.

It is completely possible in RapidMiner to use macros as parameters to the "Select Attributes" operator but there are a couple of things to bear in mind.

Firstly, when displaying the parameters for the operator, the macro's "%", "{" and "}" are suppressed from the display as shown below.

Checking the XML reveals that all is well.

Secondly, there is another more subtle point. If the macro has been defined in the process context, its value is substituted into the parameter list. So in the example above, if the macro "id_attribute" had the value "fred" in the process context, this value is explicitly placed in the operator's parameters. That's fine for a local process but it makes it impossible to execute a process containing a macro used in this way if you want to pass a different value to the macro. Fortunately, it's easy to work around. Just ensure that any macros referenced in attribute selection do not exist in the process context by creating them using the "Set Macros" operator and setting their values to those already in the context.

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