I want to concatenate these two arrays
a = np.array([[1,2,3],[3,4,5],[6,7,8]])
b = np.array([9,10,11])
such that
a = [[1,2,3,9],[3,4,5,10],[6,7,8,11]]
Tried using concatenate
for i in range(len(a)):
a[i] = np.concatenate(a[i],[b[i]])
Got an error:
TypeError: 'list' object cannot be interpreted as an integer
Tried using append
for i in range(len(a)):
a[i] = np.append(a[i],b[i])
Got another error:
ValueError: could not broadcast input array from shape (4,) into shape (3,)
(New to stackoverflow, sorry if I didn't format this well)
You can use hstack
and vector broadcasting for that:
a = np.array([[1,2,3],[3,4,5],[6,7,8]])
b = np.array([9,10,11])
res = np.hstack((a, b[:,None]))
print(res)
Output:
[[ 1 2 3 9]
[ 3 4 5 10]
[ 6 7 8 11]]
Note that you cannot use concatenate
because the array have different shapes . hstack
stack horizontally the multi-dimentional arrays so it just add a new line at the end here. A broadcast operation ( b[:,None]
) is needed so that the appended vector is a vertical one.
You can do it like this:
np.append(a,b.reshape(-1,1),axis=1)
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