I have a numpy array
a = ([[1,2,3],
[2,2,2],
[1,5,3],
[3,3,1]])
swap1 = [2,2,2]
swap2 = [3,3,1]
I want to swap the rows which are equal to swap1 and swap2 without being aware of the index of these 2 rows. I want the output to look like this
Out = ([[1,2,3],
[3,3,1],
[1,5,3],
[2,2,2]])
What would be the best way to do this? I want to avoid loops if that's an option. Thanks!
>>> a = np.array([[1,2,3],
[2,2,2],
[1,5,3],
[3,3,1]])
>>> x = [2,2,2]
>>> y = [3,3,1]
Make a boolean array of the rows you are interested in
>>> xmask = np.all(a==x,axis=1)
>>> ymask = np.all(a==y,axis=1)
>>> xmask
array([False, True, False, False])
>>> ymask
array([False, False, False, True])
Then use them to change the values
>>> a[xmask] = y
>>> a[ymask] = x
>>> a
array([[1, 2, 3],
[3, 3, 1],
[1, 5, 3],
[2, 2, 2]])
>>>
If the array is square
>>> a = np.array([[1,2,3,4],
[2,2,2,9],
[1,5,3,1],
[3,3,1,8]])
>>> y = [3,3,1,8]
>>> x = [2,2,2,9]
>>> xmask = np.all(a==x,axis=1)
>>> ymask = np.all(a==y,axis=1)
>>> a[xmask,:] = y
>>> a[ymask,:] = x
My solution running on whole list, if that's what you need so all right.
def list_swap(a, swap1, swap2):
# Running on the list
for list in a:
if (list == swap1):
list = swap2
else if (list == swap2):
list = swap1
In python you can compare lists, so there is a simple function thats running on the list and changing values if she needs to.
use map its very easy.
a = map(lambda x:([3,3,1]) if x == [2,2,2] else ([2,2,2] if x == [3,3,1] else x), a)
or (according to your variables)
a = map(lambda x:(swap2) if x == swap1 else (swap1 if x == swap2 else x), a)
see no loops, a single liner and you got your result
Result.
[[1, 2, 3], [3, 3, 1], [1, 5, 3], [2, 2, 2]]
For numpy array:
import numpy as np
a = np.array([[1,2,3],
[2,2,2],
[1,5,3],
[3,3,1]])
swap1 = [2,2,2]
swap2 = [3,3,1]
id1 = np.where(np.all(a == swap1, axis = 1))
id2 = np.where(np.all(a == swap2, axis = 1))
a[id2], a[id1] = a[id1], a[id2]
print(a)
# [[1 2 3]
# [3 3 1]
# [1 5 3]
# [2 2 2]]
idxs = [ [idx, e] for idx, e in enumerate(a) if e == swap1 or e == swap2 ]
idxs[0][0], idxs[1][0] = idxs[1][0], idxs[0][0]
for i in idxs:
a[i[0]] = i[1]
print(a)
#=> [[1, 2, 3], [3, 3, 1], [1, 5, 3], [2, 2, 2]]
import numpy as np
ar=np.array([[1,2,3],[2,2,2],[1,5,3],[3,3,1]])
swap1 = [2,2,2]
swap2 = [3,3,1]
def swapfunc( x ):
if (x==swap2).all():
return swap1
else:
return x
ar=np.apply_along_axis( swapfunc, axis=1, arr=ar )
print(ar)
Output
[[1 2 3]
[2 2 2]
[1 5 3]
[2 2 2]]
