numpy备忘

numpy删除指定行列

效果：删除第2,3行和第2,3列

[[ 1  2  3  4  5]
 [ 6  7  8  9 10]			[[ 1  4  5]
 [11 12 13 14 15]    =>		 [16 19 20]
 [16 17 18 19 20]			 [21 24 25]]
 [21 22 23 24 25]]

实现

a = np.arange(1,26).reshape((5,5))
a = np.delete(a, [1,2],axis=0) # 删除行
a = np.delete(a, [1,2],axis=1) # 删除列

numpy插入一行一列

效果：在原矩阵(3x3)的最后一行和最后一列插入零向量变为4x4

[[1,2,3]         [[1,2,3,0]
 [4,5,6]   =>     [4,5,6,0]
 [7,8,9]]         [7,8,9,0]
                  [0,0,0,0]]

实现：

a = np.arange(1,10).reshape((3,3))
col = np.zeros(3)
a = np.c_[a, col] # 3x4
row = np.zeros(4)
a = np.r_[a, [row]] # 4x4