could not broadcast input array from shape (3) into shape (2)

Question

I want to simply assign 1 into all list of a ndarray.

before,

[5.2 4.1]
[6.9 3.1]
[5.9 3.2]
[5.6 2.8]
[6.7 3.3]......................

what i need,

[1 5.2 4.1]
[1 6.9 3.1]
[1 5.9 3.2]
[1 5.6 2.8]
[1 6.7 3.3]

i am trying to iterate and insert, then try to assign the returned value. but i have a problem with the shape. found the above error.

for i in range(len(X_train)):
  X_train[i] = np.insert(X_train[i], 0,1)

then i tried to reshape before loop:

X_train = X_train.reshape(len(X_train), 3)

i found this error: cannot reshape array of size 210 into shape (105,3)

but the actual shape:

>>X_train.shape

output: (105, 2)

I am looking for any solution and also the reason. thanks in advance.

hpaulj · Accepted Answer · 2021-01-03 07:44:31Z

1

From the insert docs:

>>> a = np.array([[1, 1], [2, 2], [3, 3]])
>>> a
array([[1, 1],
       [2, 2],
       [3, 3]])
>>> np.insert(a, 1, 5, axis=1)
array([[1, 5, 1],
       [2, 5, 2],
       [3, 5, 3]])

So taking your case - act on the whole array, and specify the axis:

In [184]: arr = np.random.randint(0,9,(3,2))
In [185]: arr
Out[185]: 
array([[7, 5],
       [2, 0],
       [2, 4]])
In [186]: arr1 = np.insert(arr,0,1,axis=1)   
In [187]: arr1
Out[187]: 
array([[1, 7, 5],
       [1, 2, 0],
       [1, 2, 4]])

Many of the numpy functions take an axis (or axes) parameter. Use it.

answered Jan 3, 2021 at 7:44

hpaulj

233k14 gold badges260 silver badges392 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

majid bhatti · Accepted Answer · 2021-01-05 04:10:15Z

1

One Liner:

import numpy as np
X_train = np.hstack((X_train, np.ones((X_train.shape[0], 1), dtype=X_train.dtype)))

edited Jan 5, 2021 at 4:10

answered Jan 3, 2021 at 5:13

majid bhatti

11312 bronze badges

Comments

LevB · Accepted Answer · 2021-01-03 05:32:56Z

0

Just create an array of ones and fill all but the first column with your starting array.

import numpy as np
arr = np.array(
[[5.2, 4.1],
[6.9, 3.1],
[5.9, 3.2],
[5.6, 2.8],
[6.7, 3.3]])
sh =arr.shape

new_arr = np.ones((sh[0],sh[1]+1))
new_arr[:,1:] = arr

print(new_arr)

Output :

[[1.  5.2 4.1]
 [1.  6.9 3.1]
 [1.  5.9 3.2]
 [1.  5.6 2.8]
 [1.  6.7 3.3]]

answered Jan 3, 2021 at 5:32

LevB

9537 silver badges10 bronze badges

1 Comment

dipcb05 Over a year ago

its a dataset actually, so i have to iterate

Collectives™ on Stack Overflow

could not broadcast input array from shape (3) into shape (2)

3 Answers 3

Comments

Comments

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

Comments

Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related