I have an array with the shape (10000,6). For example:
a = np.array([[5, 5, 5, 5, 5, 5][10, 10, 10, 10, 10][15, 15, 15, 15, 15]...])
I want to take every 25th array and subtract its element values from the next 25 elements until a new subtraction array in selected. so for example if the first array is:
[10, 10, 10, 10, 10]
then these values should be subtracted on the array itself and the next 25 arrays until for example a new subtraction array like this is selected:
[2, 2, 2, 2, 2]
then the array itself and the following 25 elements should be subtracted that arrays values. This means that after the operation every 25th array will be:
[0, 0, 0, 0, 0]
because it has been subtracted by itself.
CodePudding user response:
Here's what I would do:
import numpy as np
arr = np.random.randint(0, 10, (9, 3))
group_size = 3
# select vectors you want ot subtract and copy them {group_size} times
selected = arr[::group_size].repeat(3, axis = 0)
# subtract selected vectors from all vectors in the group
sub_arr = arr-selected
output:
arr =
[[9 6 3]
[8 3 3]
[2 0 4]
[0 3 9]
[3 9 9]
[0 8 6]
[4 0 0]
[6 1 9]
[2 6 4]]
selected =
[[9 6 3]
[9 6 3]
[9 6 3]
[0 3 9]
[0 3 9]
[0 3 9]
[4 0 0]
[4 0 0]
[4 0 0]]
sub_arr =
[[ 0 0 0]
[-1 -3 0]
[-7 -6 1]
[ 0 0 0]
[ 3 6 0]
[ 0 5 -3]
[ 0 0 0]
[ 2 1 9]
[-2 6 4]]
CodePudding user response:
You can reshape your array so that each chunk has the right number of lines, and then simply subtract the first line
import numpy as np
a = np.arange(10000)[:, None] * np.ones(6)
a = a.reshape(-1, 25, 6)
a -= a[:, 0, :][:, None, :]
a = a.reshape(-1, 6)