Find arrays with the shortest distance

Question

I have a array_objetivo and would like to find the id and the distance (Euclidean in this example) of n arrays closer to him that are in array_all. Following are examples of arrays.

array_objetivo = np.array([2,2,3,4])

array_all = np.array([[1,1,2,2],
                      [2,2,3,3],
                      [3,3,4,4],
                      [4,4,5,5]])

To find only the nearest, I did:

def calcula_distancia(array1, array2):
    # Distância Euclidiana
    return np.linalg.norm(array1-array2)

def pega_vetor_mais_proximo(array_objetivo, array_all):

    menor_dist = calcula_distancia(array_objetivo, array_all[0])
    id_menor_dist = 0

    for i in range(1, array_all.shape[0]):
        dist = calcula_distancia(array_objetivo, array_all[i])
        if dist < menor_dist:
            menor_dist = dist
            id_menor_dist = i

    return menor_dist, id_menor_dist

How can I modify to find the n nearest array efficiently?

Answer 1

I can’t type a code in here the way I’d like but I think I can help you.

You create an empty list and a while loop based on a counter that will receive the amount of distances you want to return, inside that while you put your loop for the way it is in the code and at the end of that go you decrement your counter and delete from the list the distance you found, if your array_all is a list that cannot be modified you simply create a local variable that receives array_all and do what you were told.

Answer 2

I was able to solve by calculating all distances and storing them. Then, I get the ids of the lowest values from the distance list and the returns.

def pega_n_vetores_mais_proximos(array_objetivo, array_all, n):
    distancias = []

    # calcula todas as distâncias e as armazena
    for i in range(0, array_all.shape[0]):
        distancias.append(calcula_distancia(array_objetivo,array_all[i]))

    distancias = np.array(distancias)

    # pega os ids das menores distâncias
    menores_n_idx = np.argsort(distancias)[:n]

    return distancias[menores_n_idx], menores_n_idx