Collect List Block

Where Is It?

The Collect List block is located in the data statements drawer of the Blawx toolbox, in the List subdrawer.

What Does It Do?

The Collect List Block is used to generate a list from (or test that a list matches) the bindings of a certain variable in a set of statements.

It is used primarily when there are a number of values in your data, and they need to be combined into a list in order to perform aggregate functions on them, such as counting how many there are, or taking their sum or average.

Technical Details

The Collect List Block is a statement block and can be stacked with other statement blocks. It expects two variable inputs, and one statement input. The first variable is shared with the other statements in the same stack as the Collect List Block, and can be thought of as the output variable. The second variable must be a variable that is used inside the statements. The statements must use the variable provided in the second input.

The block causes the reasoner to run the statements included in the block, and get all of the answers that would have been returned if those statements had been run as a question. It then takes all of the values for the variable in the second input, and turns them into a list. That list is bound to the variable name in the first input, and can be used in the rest of your code.

Tips

Whereas when running a question in Blawx results in different explanations for the same bindings being collected as a single "answer", the Collect List Block does not know whether repeating values are significant, and so it includes all duplicates as many times as they are found.