Get closest value array for array of arrays.

Get closest value array for array of arrays. - Printable Version

+- Python Forum (https://python-forum.io)
+-- Forum: Python Coding (https://python-forum.io/forum-7.html)
+--- Forum: General Coding Help (https://python-forum.io/forum-8.html)
+--- Thread: Get closest value array for array of arrays. (/thread-22559.html)

Get closest value array for array of arrays. - DreamingInsanity - Nov-17-2019

Title is quite confusing let me explain:
If I have an 2D array of values 'y': [[10,20,10],[30,20,10],[10,10,10],[45,37,34]]
and a singular array 'x': [25,18,9]
I want to be able to run function findClosestArray(x, y) which will return

Output:
[30,20,10]

because that is the closest array to the one I provided.
If I ran findClosestArray(x, y) with 'x' NOW being [43,37,30] it would return

Output:
[45,37,34]

It's very similar to this:

myList = [6,6,10,50,24,457,24]
myNumber= 9
a = min(myList, key=lambda x:abs(x-myNumber))
print(a)

(which would return 10)
but instead with arrays.

How can I do this?

RE: Get closest value array for array of arrays. - DeaD_EyE - Nov-18-2019

(Nov-17-2019, 09:31 PM)DreamingInsanity Wrote: It's very similar to this:
myList = [6,6,10,50,24,457,24]
myNumber= 9
a = min(myList, key=lambda x:abs(x-myNumber))
print(a)
(which would return 10)
but instead with arrays.

How can I do this?

To use min, was already the right way, also the use of abs. The key is used to get for each element one or more values to compare.

def find_closest(x, array2d):
    x_sum = sum(x)
    ###
    diffs = [sum(y) - x_sum for y in array2d]
    print(diffs)
    # just for demonstration
    ###
    result = min(array2d, key=lambda z: abs(sum(z) - x_sum))
    index = array2d.index(result)
    return index, result

If you don't need the index and the debugging information, the function looks like this.

def find_closest(x, array2d):
    x_sum = sum(x)
    return min(array2d, key=lambda z: abs(sum(z) - x_sum))

For fun you can implement other functions for comparison.
If the lists are for example points, you can calculate the longest and shortest distances to other points:

x1, y1, z1 = 4, 5, 9
x2, y2, z2 = 40, 50, 90
dist = math.sqrt( (x2 - x1) ** 2 + (y2 - y1) ** 2 + (z2 - z1) ** 2 )

With Python 3.8 we got some nice changes in the math module.
For example the hypot function accepts now more than two arguments.

hypot(*coordinates) -> value

Multidimensional Euclidean distance from the origin to a point.

Roughly equivalent to:
    sqrt(sum(x**2 for x in coordinates))

For a two dimensional point (x, y), gives the hypotenuse
using the Pythagorean theorem:  sqrt(x*x + y*y).

For example, the hypotenuse of a 3/4/5 right triangle is:

    >>> hypot(3.0, 4.0)
    5.0
Type:      builtin_function_or_method

With this function, it's a bit lesser code:

dist2 = math.hypot(x2-x1, y2-y1, z2-z1)

And to calculate distances between points, we've now a convenience function.

Signature: math.dist(p, q, /)
Docstring:
Return the Euclidean distance between two points p and q.

The points should be specified as sequences (or iterables) of
coordinates.  Both inputs must have the same dimension.

Roughly equivalent to:
    sqrt(sum((px - qx) ** 2.0 for px, qx in zip(p, q)))
Type:      builtin_function_or_method

Using the function:

point1 = (x1, y1, z1)
point2 = (x2, y2, z2)
dist3 = math.dist(point1, point2)

Instead of using sum to calculate the sum of the list, you could use key=lambda z: math.dist(x, z).

By the way, Python is also very useful to solve homework with code, which the teacher could understand.

RE: Get closest value array for array of arrays. - DreamingInsanity - Nov-18-2019

Thanks a lot for this!
It was actually for RGB values but I didn't know about the new python 3.8 function, so that's cool.

I see that you are totalling all the values in the arrays. As I was going to sleep I had a similar thought, but didn't actually know that it was going to work or how I could at least pull it off in a semi-efficient manner.

Thanks again,
Dream