沿着NumPy数组的行在特定位置插入零行

Question

我有一个两列numpy数组.我想通过第2列的每一行,并取每组2个数字(9.6-0,19.13-9.6等)之间的差异.如果差值> 15,我想为两列插入一行0.我真的只需要在第一列中结束值(我只需要第二列来确定将0放在哪里),所以如果更容易将它们拆分,那就没问题了.

这是我的输入数组:

 [[0.00 0.00]
 [1.85 9.60]
 [2.73 19.13]
 [0.30 28.70]
 [2.64 38.25]
 [2.29 47.77]
 [2.01 57.28]
 [2.61 66.82]
 [2.20 76.33]
 [2.49 85.85]
 [2.55 104.90]
 [2.65 114.47]
 [1.79 123.98]
 [2.86 133.55]]

它应该变成:

 [[0.00 0.00]
 [1.85 9.60]
 [2.73 19.13]
 [0.30 28.70]
 [2.64 38.25]
 [2.29 47.77]
 [2.01 57.28]
 [2.61 66.82]
 [2.20 76.33]
 [2.49 85.85]
 [0.00 0.00]
 [2.55 104.90]
 [2.65 114.47]
 [1.79 123.98]
 [2.86 133.55]]

Answer 1

您可以使用一个衬垫做ediff1d,argmax并且insert从numpy:

np.insert(arr, np.argmax(np.append(False, np.ediff1d(arr[:,1])>15)), 0, axis=0)

#array([[   0.  ,    0.  ],
#       [   1.85,    9.6 ],
#       [   2.73,   19.13],
#       [   0.3 ,   28.7 ],
#       [   2.64,   38.25],
#       [   2.29,   47.77],
#       [   2.01,   57.28],
#       [   2.61,   66.82],
#       [   2.2 ,   76.33],
#       [   2.49,   85.85],
#       [   0.  ,    0.  ],
#       [   2.55,  104.9 ],
#       [   2.65,  114.47],
#       [   1.79,  123.98],
#       [   2.86,  133.55]])

Answer 2

假设A作为输入数组,这是一个基于零初始化的矢量化方法 -

# Get indices at which such diff>15 occur 
cut_idx = np.where(np.diff(A[:,1]) > 15)[0]

# Initiaize output array
out = np.zeros((A.shape[0]+len(cut_idx),2),dtype=A.dtype)

# Get row indices in the output array at which rows from A are to be inserted.
# In other words, avoid rows to be kept as zeros. Finally, insert rows from A.
idx = ~np.in1d(np.arange(out.shape[0]),cut_idx + np.arange(1,len(cut_idx)+1))
out[idx] = A

样本输入,输出 -

In [50]: A  # Different from the one posted in question to show variety
Out[50]: 
array([[   0.  ,    0.  ],
       [   1.85,    0.6 ],
       [   2.73,   19.13],
       [   2.2 ,   76.33],
       [   2.49,   85.85],
       [   2.55,  104.9 ],
       [   2.65,  114.47],
       [   1.79,  163.98],
       [   2.86,  169.55]])

In [51]: out
Out[51]: 
array([[   0.  ,    0.  ],
       [   1.85,    0.6 ],
       [   0.  ,    0.  ],
       [   2.73,   19.13],
       [   0.  ,    0.  ],
       [   2.2 ,   76.33],
       [   2.49,   85.85],
       [   0.  ,    0.  ],
       [   2.55,  104.9 ],
       [   2.65,  114.47],
       [   0.  ,    0.  ],
       [   1.79,  163.98],
       [   2.86,  169.55]])