I have a numpy vector
, and a numpy array
.
我有一个numpy向量和一个numpy数组。
I need to take from every row in the matrix the first N (lets say 3) values that are smaller than (or equal to) the corresponding line in the vector.
我需要从矩阵中的每一行获取小于(或等于)向量中相应行的第一个N(比如3)值。
so if this is my vector:
所以如果这是我的载体:
7,
9,
22,
38,
6,
15
and this is my matrix:
这是我的矩阵:
[[ 20., 9., 7., 5., None, None],
[ 33., 21., 18., 9., 8., 7.],
[ 31., 21., 13., 12., 4., 0.],
[ 36., 18., 11., 7., 7., 2.],
[ 20., 14., 10., 6., 6., 3.],
[ 14., 14., 13., 11., 5., 5.]]
the output should be:
输出应该是:
[[7,5,None],
[9,8,7],
[21,13,12],
[36,18,11],
[6,6,3],
14,14,13]]
Is there any efficient way to do that with masks or something, without an ugly for
loop?
是否有任何有效的方法来做掩码或其他东西,没有丑陋的for循环?
Any help will be appreciated!
任何帮助将不胜感激!
1 个解决方案
#1
3
Approach #1
Here's one with broadcasting
-
这是一个广播 -
def takeN_le_per_row_broadcasting(a, b, N=3): # a, b : 1D, 2D arrays respectively
# First col indices in each row of b with <= corresponding one in a
idx = (b <= a[:,None]).argmax(1)
# Get all N ranged column indices
all_idx = idx[:,None] + np.arange(N)
# Finally advanced-index with those indices into b for desired output
return b[np.arange(len(all_idx))[:,None], all_idx]
Approach #2
Inspired by NumPy Fancy Indexing - Crop different ROIs from different channels
's solution, we can leverage np.lib.stride_tricks.as_strided
for efficient patch extraction, like so -
受NumPy花式索引的启发 - 从不同渠道的解决方案中获取不同的投资回报率,我们可以利用np.lib.stride_tricks.as_strided进行有效的补丁提取,如下所示 -
from skimage.util.shape import view_as_windows
def takeN_le_per_row_strides(a, b, N=3): # a, b : 1D, 2D arrays respectively
# First col indices in each row of b with <= corresponding one in a
idx = (b <= a[:,None]).argmax(1)
# Get 1D sliding windows for each element off data
w = view_as_windows(b, (1,N))[:,:,0]
# Use fancy/advanced indexing to select the required ones
return w[np.arange(len(idx)), idx]
#1
3
Approach #1
Here's one with broadcasting
-
这是一个广播 -
def takeN_le_per_row_broadcasting(a, b, N=3): # a, b : 1D, 2D arrays respectively
# First col indices in each row of b with <= corresponding one in a
idx = (b <= a[:,None]).argmax(1)
# Get all N ranged column indices
all_idx = idx[:,None] + np.arange(N)
# Finally advanced-index with those indices into b for desired output
return b[np.arange(len(all_idx))[:,None], all_idx]
Approach #2
Inspired by NumPy Fancy Indexing - Crop different ROIs from different channels
's solution, we can leverage np.lib.stride_tricks.as_strided
for efficient patch extraction, like so -
受NumPy花式索引的启发 - 从不同渠道的解决方案中获取不同的投资回报率,我们可以利用np.lib.stride_tricks.as_strided进行有效的补丁提取,如下所示 -
from skimage.util.shape import view_as_windows
def takeN_le_per_row_strides(a, b, N=3): # a, b : 1D, 2D arrays respectively
# First col indices in each row of b with <= corresponding one in a
idx = (b <= a[:,None]).argmax(1)
# Get 1D sliding windows for each element off data
w = view_as_windows(b, (1,N))[:,:,0]
# Use fancy/advanced indexing to select the required ones
return w[np.arange(len(idx)), idx]