在python矩阵中将上三角复制到下三角 [英] Copy upper triangle to lower triangle in a python matrix

问题描述

       iluropoda_melanoleuca  bos_taurus  callithrix_jacchus  canis_familiaris
ailuropoda_melanoleuca     0        84.6                97.4                44
bos_taurus                 0           0                97.4              84.6
callithrix_jacchus         0           0                   0              97.4
canis_familiaris           0           0                   0                 0

这是我拥有的python矩阵的简短版本.我在上方的三角形中有此信息.是否有一个简单的函数将矩阵的上三角复制到下三角?

This is a short version of the python matrix I have. I have the information in the upper triangle. Is there an easy function to copy the upper triangle to the down triangle of the matrix?

推荐答案

要在NumPy中执行此操作，而无需使用双循环，可以使用

To do this in NumPy, without using a double loop, you can use tril_indices.

>>> i_lower = np.tril_indices(n, -1)
>>> matrix[i_lower] = matrix.T[i_lower]  # make the matrix symmetric

请注意，不要尝试混用tril_indices和 triu_indices ，因为它们都使用行主索引，即，这行不通:

Be careful that you do not try to mix tril_indices and triu_indices as they both use row major indexing, i.e., this does not work:

>>> i_upper = np.triu_indices(n, 1)
>>> i_lower = np.tril_indices(n, -1)
>>> matrix[i_lower] = matrix[i_upper]  # make the matrix symmetric
>>> np.allclose(dist.T, dist)
False

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