WhileIterator

The WhileIterator allows you to group a set of gems together, and then run them one after another repeatedly in a loop.

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Input

The input of the WhileIterator can be any dataset. Importantly, the output schema of the WhileIterator must match or be a subset of the input schema. This is because the output feeds back into the input as the subgraph is iterating (looping).

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Configuration

Once you have a WhileIterator subgraph on your canvas, set configurations by opening the subgraph and clicking on Configuration. The following table describes the parameters you need to set.

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Subgraph

Within the WhileIterator, you can design a flow with multiple gems to create your desired output. Importantly, you also need to understand the two inputs of the WhileIterator_Output. The order of your inputs is important:

• The in0 dataset contains the DataFrame for the following iteration. If this dataset becomes empty, the loop is terminated.
• The in1 dataset passes on an individual iteration. You’ll see the entire list of iterations as the output of the WhileIterator gem.

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Break condition

There are two scenarios in which the WhileIterator will break:

• The in0 dataset of the WhileIterator_Output becomes empty.
• The maximum number of iterations is reached.

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Output

There are two outputs of the WhileIterator:

• The out0 dataset that contains the output of the last iteration of the WhileIterator.
• The out1 dataset that contains the whole list of iterations produced by the WhileIterator. This is produced by performing a union on all output iterations.

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Example

Imagine you are simulating an investment that earns a fixed percentage of interest per year. You want to keep compounding the interest until your investment reaches a desired amount. You can use the WhileIterator gem to produce a dataset demonstrating this yearly growth. For this example, the input of the WhileIterator will be a simple table that describes your starting investment and the fixed interest rate.

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Add Reformat gem

Now, let’s use a Reformat gem in the WhileIterator subgraph to update the Year and Principal each iteration.

1. Add the Reformat gem inside the WhileIterator.
2. Connect WhileIterator_Input to the Reformat gem.
3. Connect the Reformat gem to the WhileIterator_Output.
4. Configure the Expressions table as it is shown below.

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Terminate loop

The while loop will stop if the in0 dataset becomes empty. How can the in0 dataset become empty? In this example:

1. Add a Filter gem with the condition principal < 2000.
2. Connect the Reformat gem output to the input of the Filter gem.
3. Connect the Filter gem output to the input of WhileIterator_Output.

This way, the Filter gem will return data as-is until the principal reaches 2000. After that, the record is filtered out, and the loop will terminate.

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View output data

The out0 dataset should be empty because we used a Filter gem to return an empty set when the principal > 2000. Below is an example out1 dataset. This lets you project how your principal will grow over the years.