For a given 2D vector described by cartesian coordinates of its initial point and terminal point in the following format:
```python
[[x1, y1], [x2, y2]]
```
Your function must return this vector's length represented as a floating point number.
Error must be within 1e-7.
Coordinates can be integers or floating point numbers.
def vector_length(vector):
    return sum((a - b)**2 for a,b in zip(*vector))**0.5
def vector_length(vector):
    return sum((a - b)**2 for a,b in zip(*vector))**0.5