Change Indexer __init__ to start at -1

[PascalLesage]

Fixes https://github.com/PascalLesage/brightway2-presamples/issues/47

[PascalLesage]

Need to change tests first. Should get agreement on this first.

[cmutel]

@PascalLesage I know that we discussed this earlier (See email chain "Stupid indexers hurt my brain" from March 5, 2018).

I am no longer familiar enough with the code to understand why we couldn't just take this approach at the very beginning. My hunch is that it is due to compatibility with static LCA calculations. However, there is a clear need for MC to start with the first column, so we will find a way. I will need a bit of time to really understand this, though.

[cmutel]

I think the updated code is a better path. It works with https://bitbucket.org/cmutel/brightway2-calc/commits/a3ca3d60ac11c009776b712202a8cbe99b41cd46.

Here is how the indexers get instantiated and used with my proposed changes:

LCA: .__init__(): Create self.presamples, instance of PackageDataLoader

.load_lci_data(): self.presamples.update_matrices(lci matrices) -> Doesn't update indices because specified matrices

.load_lcia_data():self.presamples.update_matrices(lcia matrices) -> Doesn't update indices because specified matrices

PackagesDataLoader: .__init__(): self.load_data -> creates instances of Indexer (self.sample_indexers)

.update_matrices(): self.update_sample_indices (if for all matrices andadvance_indicesflag)

.update_sample_indices(): next(indexer) for indexer in self.sample_indexers sets self.index to self.count % self.ncols (if sequential) or random

.reset_sequential_indices():

for indexer in self.sample_indexers:
    indexer.reset_sequential_indices()

Indexer: .__init__():

• sets self.index to None
• sets self.count to 0

Monte Carlo: .load_data():

LCA.load_lci_data()
if self.presamples:
    self.presamples.reset_sequential_indices()

.__next__(): self.presamples.update_matrices()

[coveralls]

Pull Request Test Coverage Report for Build 97

• 4 of 6 (66.67%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.2%) to 95.199%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
presamples/loader.py	1	3	33.33%
<!--	Total:	4	6	66.67%	-->

Totals
Change from base Build 91:	-0.2%
Covered Lines:	813
Relevant Lines:	854

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💛 - Coveralls

[PascalLesage]

Much better indeed.