How do I assign label to array rows?-CodePudding

I have an array A with size 600x6 that each row is a vector and I want to calculate the distance of each row from all other rows of the array. calculating the distance ( BD distance) is easy and I can calculate all the distances and put them in a matrix D(600x600), but during my code, I have just the value of the row not the index of it and so I cannot use D to find the distance quickly. so I have to calculate the distance again. my question is it a way to assign a label or index to each row of A during the code? for example, I have A1 and A2 so I very fast find out that I have to extract D1,2 for distance. I am not very familiar with python. Could you please tell me how can I do this without calculating the distance each time? as you can see in the following code, the centroid during the next step of the code will change. so I have to calculate the BD distance again which is time-consuming. but if I could save the index of centroid I could extract the distance from my distance matrix very fast.

def kmeans_BD(psnr_bitrate,K,centroid):
    m=psnr_bitrate.shape[0]#number of samples
    n=psnr_bitrate.shape[1]#number of bitrate
    
    # creating an empty array
    BD=np.zeros((m,K))
    #weight of BD_rate
    wr=0.5
    #weight of BD_Q
    wq=0.5
    n_itr=10
    # finding distance between for each centroid
    for itr in range(n_itr):
        for k in range(K):
            for i in range(len(psnr_bitrate)):
                BD_R=bd_rate(rate,centroid[k,:],rate,psnr_bitrate[i,:])
                if BD_R==-2:
                    BD_R=np.inf
                BD_Q=bd_PSNR(rate,centroid[k,:],rate,psnr_bitrate[i,:])
                if BD_Q==-2:
                    BD_Q=np.inf
                BD[i,k]=np.abs(wr*BD_R wq*BD_Q)

CodePudding user response：

Check out the code provided below for a method allowing to achieve what you want. If there is no .index() method available for the matrix objects the code provide a getIndex() function to get the index of an item in an iterable. The code provide a getDistance() function with which the distance between two vectors can be got from the distance matrix D created from vector matrix A. If there is an .index() method available replace getIndex(A, vector) with vector.index() for both vectors in getDistance():

def getDistance(vector_1, vector_2, vector_matrix_A, distance_matrix_D):
    try: 
        distance = distance_matrix_D[
            getIndex(A, vector_1)]
           [getIndex(A, vector_2)]
        return distance
    except:
        return None

def getIndex(vectorArray, vector):
    for indx, item in enumerate(vectorArray):
        if item == vector:
            return indx
    return None

A = [ [i*item for i in (range(1,4))] for item in range(1,7)]
print(f'{A=}')
assert A == [[1, 2, 3], [2, 4, 6], [3, 6, 9], [4, 8, 12], [5, 10, 15], [6, 12, 18]]
vector = A[2]                    
print(f'{vector=}')              # [3, 6, 9]
assert A.index(vector) == 2
print(f'index of {vector} in A using A.index(vector)    : {A.index(vector)}')

assert getIndex(A, vector) == 2
print(f'index of {vector} in A using getIndex(A, vector): {getIndex(A, vector)}')

D = []
for row in range(6):
    column = []
    for colval in range(1 6*row,7 6*row):
        column.append(colval)
    D.append(column)
assert D == [
              [ 1,  2,  3,  4,  5,  6], 
              [ 7,  8,  9, 10, 11, 12], 
              [13, 14, 15, 16, 17, 18], 
              [19, 20, 21, 22, 23, 24], 
              [25, 26, 27, 28, 29, 30], 
              [31, 32, 33, 34, 35, 36],
            ]

vector_3 = A[3]
vector_5 = A[5]
print(f'distance between {vector_3}, {vector_5} is: '
      f'{getDistance(vector_3, vector_5, A, D)}' )
assert getDistance(vector_3, vector_5, A, D) == 24

CodePudding user response：

if we change the answer that Claudio suggested, it will work for me.

def getDistance(vector_1, vector_2, vector_matrix_A, distance_matrix_D):
    try: 
        distance = distance_matrix_D[getIndex(vector_matrix_A, vector_1),getIndex(vector_matrix_A, vector_2)]
        return distance
    except:
        return None

def getIndex(vectorArray, vector):
    indx,=np.where(np.all(vectorArray==vector,axis=1))
    return indx