[英]Vectorize compressed sparse matrix from array in Python
我正在尝试将图论方法应用于图像处理问题。 我想从包含要绘制的点的数组生成邻接矩阵。 我想生成数组中点的完整图形。 如果阵列中需要绘制N个点,则需要一个NxN矩阵。 权重应该是点之间的距离,所以这是我的代码:
''' vertexarray is an array where the points that are to be
included in the complete graph are True and all others False.'''
import numpy as np
def array_to_complete_graph(vertexarray):
vertcoords = np.transpose(np.where(vertexarray == True))
cg_array = np.eye(len(vertcoords))
for idx, vals in enumerate(vertcoords):
x_val_1, y_val_1 = vals
for jdx, wals in enumerate(vertcoords):
x_diff = wals[0] - vals[0]
y_diff = wals[1] - vals[1]
cg_array[idx,jdx] = np.sqrt(x_diff**2 + y_diff**2)
return cg_array
当然,这可行,但是我的问题是:可以在不嵌套for循环的情况下生成相同的数组吗?
使用函数scipy.spatial.distance.cdist()
:
import numpy as np
def array_to_complete_graph(vertexarray):
vertcoords = np.transpose(np.where(vertexarray == True))
cg_array = np.eye(len(vertcoords))
for idx, vals in enumerate(vertcoords):
x_val_1, y_val_1 = vals
for jdx, wals in enumerate(vertcoords):
x_diff = wals[0] - vals[0]
y_diff = wals[1] - vals[1]
cg_array[idx,jdx] = np.sqrt(x_diff**2 + y_diff**2)
return cg_array
arr = np.random.rand(10, 20) > 0.75
from scipy.spatial.distance import cdist
y, x = np.where(arr)
p = np.c_[x, y]
dist = cdist(p, p)
np.allclose(array_to_complete_graph(arr), dist)
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