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Select
(RapidMiner Studio Core)
Synopsis
This operator returns the specified single object from the given collection of objects.Description
Operators like the Collect operator combine a variable number of input objects into a single collection. In the Process View, collections are indicated by double lines. The Select operator can be used for selecting an individual object from this collection. The index parameter specifies the index of the required object. If the objects of the given collection are collections themselves the output of this operator would be the collection at the specified index. However if the unfold parameter is set to true the index refers to the index in the flattened list, i.e. the list obtained from the input list by replacing all nested collections by their elements.
Collections can be useful when you want to apply the same operations on a number of objects. The Collect operator will allow you to collect the required objects into a single collection, the Loop Collection operator will allow you to iterate over all collections and finally you can separate the input objects from a collection by individually selecting the required element by using the Select operator.
Input
collection (Collection)This port expects a collection of objects as input. Operators like the Collect operator combine a variable number of input objects into a single collection.
Output
selected (IOObject)The object at the index specified by the index parameter is returned through this port.
Parameters
- indexThis parameter specifies the index of the required object within the collection of objects. Range: integer
- unfoldThis parameter is only applicable when the objects of the given collection are collections themselves. This parameter specifies whether collections received at the input ports should be considered unfolded for selection. If the input objects are collections themselves and the unfold parameter is set to false, then the index parameter will refer to the collection at the specified index. However if the unfold parameter is set to true then the index refers to the index in the flattened list, i.e. the list obtained from the input list by replacing all nested collections by their elements. Range: boolean
Tutorial Processes
Introduction to collections
This Example Process explains a number of important ideas related to collections. It shows how objects can be collected into a collection, then some preprocessing is applied on the collection and finally individual elements of the collection are separated as required.
The 'Golf' and 'Golf-Testset' data sets are loaded using the Retrieve operator. Both ExampleSets are provided as inputs to the Subprocess operator. The subprocess performs some preprocessing on the ExampleSets and then returns them through its output ports. The first output port returns the preprocessed 'Golf' data set which is then used as training set for the Decision Tree operator. The second output port delivers the preprocessed 'Golf-Testset' data set which is used as testing set for the Apply Model operator which applies the Decision Tree model. The performance of this model is measured and it is connected to the results port. The training and testing ExampleSets can also be seen in the Results Workspace.
Now have a look at the subprocess of the Subprocess operator. First of all, the Collect operator combines the two ExampleSets into a single collection. Note the double line output of the Collect operator which indicates that the result is a collection. Then the Loop Collection operator is applied on the collection. The Loop Collection operator iterates over the elements of the collection and performs some preprocessing (renaming an attribute in this case) on them. You can see in the subprocess of the Loop Collection operator that the Rename operator is used for changing the name of the Temperature attribute to 'New Temperature'. It is important to note that this renaming is performed on both ExampleSets of the collection. The resultant collection is supplied to the Multiply operator which generates two copies of the collection. The first copy is used by the Select operator (with index parameter = 1) to select the first element of the collection i.e. the preprocessed 'Golf' data set. The second copy is used by the second Select operator (with index parameter = 2) to select the second element of the collection i.e. the preprocessed 'Golf-Testset' data set.
