Way to relate initial seed to output at the end of an operation chain

[gchqdev03]

It would be really useful if there was a way to relate the results of a multihop operation chain to the initial seeds that were passed into the chain. If the operation chain has more than one operation and the end result elements/objects do not have an identifier that is easily relatable to any of the seeds that were passed in, then it is difficult to know which seeds resulted in which answers

[p013570]

This is linked to #1301.

[p013570]

After #1301 is done, we should then be able to create an Operation perhaps called 'ExtractItems'.
This would take an Iterable of Iterables and and returns an Iterable if the extracted item.

E.g
Input =
[
[1a, 2a, 3a],
[1b, 2b, 3b],
[1c, 2b, 3c]
]

and we ask to extract the second item out of the iterables then the result would be:
[2a, 2b, 2c]

This would allow us to create an Operation Chain like this:
Path(some seeds),
ExtractItems(0) - extract the first edge in each path
ToVertices(MATCHED_VERTEX) - this extracts the original seeds

@gchqdev03 - would that work for you?

[javadev001001]

@p013570 I think that would work for our use-case. It'd be nice to be able to very easily 'pick up' properties as you traverse, but perhaps that's a separate issue?

[p013570]

OK great. However, @javadev001001 - I'm not sure what you mean by 'pick up' properties?

[m607123]

Just to clarify the desired behaviour for the extraction of items..
Given that the GetWalks (what was Path) operation could potentially return a Walk containing a Set of 2+ edges with the same source/destination, would one expect the output to :

• contain as many extracted vertices as there are edges in this set, or
• deduplicate these vertices so no matter the number of edges between the source/dest, the output only contains two vertices to represent all of the edges

[p013570]

@m607123 the way your code currently looks seems to be going in the right direction. It allows users to plug in any map Function or flatMap Function so they can extract whatever they want.

So I would imagine they would do something like:

• GetWalks
  This would return something like:

[
    [[1-2], [2-3], [3-4]],
    [[1-5], [5-6], [6-7]]
]

• FlatMap(FirstItem)

This would return:

[
    [1-2],
    [1-5]
]

• FlatMap(FirstItem)
  This would return:

[
    1-2,
    1-5
]

• Map(Extract matched vertex - this might need to be a new function)
  Which would return:

[
    1,
    1
]

• ToSet
  The deduplicated results:

[
    1
]

A bit complicated but quite descriptive. Perhaps we could have a function that merges the first 2 flatmap operations into 1.

[p013570]

Merged into develop.