fixing the negative_samples notebook

[potipot]

• added recordcollection add operator (+)
• add slicing (slice indexing) for RecordCollection to return a new object of the same class
• fix the negative samples notebook
• add tests for the new operator
• fix failing tests

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[FraPochetti]

A couple of tests are not passing apparently.

[FraPochetti]

why are the changes to RecordCollection needed?

[potipot]

These changes allow more intuitive use of the old records list, a bit like regular lists. This slicing and adding is used in the negative samples notebook, but I also came across this use case and already had these commits in my own branch done some time before.

The idea is to be able to

• do RecordCollection + RecordCollection
• and make sure that RecordCollection[:n] returns a new RecordCollection instance (and not List[BaseRecord]), cause then we cannot do RecordCollection + RecordCollection[:10] (Operator + not defined for RC and List)

TODO;

You;re right I hurried too much with the PR. I will add tests to the new operator and fix the ones failing.

[potipot]

the failing tests are the known efficientdet metric values

[fstroth]

Looks good to me. @FraPochetti I think we can merge.

[FraPochetti]

Looks good to me. @FraPochetti I think we can merge.

Yes! Let's merge!