Sort/index according to closeness to a point

[Ruibin-Liu]

Currently, points or coordinates are sorted by the first dimension first and then the next dimensions. This makes the indexing/pseudo-grouping start from a corner and end at the furthest opposite corner. There is nothing wrong to organize the data in this way but it's interesting whether we can start from an arbitrary point and pseudo group points around it according to their distances to it.

Thoughts:

1. Transform each data points around the chosen point by absolute difference in each direction;
2. Sort the transformed data;
3. Transform the data back to their original values but keep the indexing.