Tweaks to Page Rank
Tweaks to Page Rank

- Replace `var` with `let`
- Use `eles.byGroup()` to avoid double iteration for getting nodes and edges lists
- Avoid redundant ID calls
- Avoid `filter()` call by skipping loops inline
- Use multiplication instead of `Math.pow()` for squaring
- Improvement of ~1.07x

Ref #1224

cytoscape/cytoscape.js,cytoscape/cytoscape.js