[Struct] Refactor sparse

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (06dc911) 89.45% compared to head (43c51e3) 99.31%. Report is 2 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #416 +/- ## ========================================== + Coverage 89.45% 99.31% +9.86% ========================================== Files 125 126 +1 Lines 8342 8352 +10 ========================================== + Hits 7462 8295 +833 + Misses 880 57 -823 ``` | [Flag](https://app.codecov.io/gh/massquantity/LibRecommender/pull/416/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=massquantity) | Coverage Δ | | |---|---|---| | [CI](https://app.codecov.io/gh/massquantity/LibRecommender/pull/416/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=massquantity) | `99.31% <100.00%> (+9.86%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=massquantity#carryforward-flags-in-the-pull-request-comment) to find out more.

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