I have an array (b) and I want to add new rows according to the position of 1s in the (a) array.
a=np.array([1,1,0,1,0]
b=np.array([1,2,3,4,5])
I'd need to make a new array like this:
Output: array([1,2,3,4,5],[1,0,0,0,0],[0,1,0,0,0],[0,0,0,1,0])
How could this be done? Loop and append? Many thanks in advance
def solution(a, b):
result = [b]
for i, elem in enumerate(a):
if elem == 1:
temp = [0] * len(a)
temp[i] = 1
result.append(temp)
return np.array(result)
One-liner with broadcasting -
In [14]: np.vstack((b,np.arange(len(a)) == np.flatnonzero(a)[:,None]))
Out[14]:
array([[1, 2, 3, 4, 5],
[1, 0, 0, 0, 0],
[0, 1, 0, 0, 0],
[0, 0, 0, 1, 0]])
With zeros-initialized array -
In [17]: s = a.sum()
In [18]: c = np.zeros((s,len(a)),dtype=b.dtype)
In [20]: c[np.arange(s),np.flatnonzero(a)] = 1
In [21]: np.vstack((b,c))
Out[21]:
array([[1, 2, 3, 4, 5],
[1, 0, 0, 0, 0],
[0, 1, 0, 0, 0],
[0, 0, 0, 1, 0]])
