How can I add a column containing only "1" to the beginning of a second numpy array.
X = np.array([1, 2], [3, 4], [5, 6])
I want to have X become
[[1,1,2], [1,3,4],[1,5,6]]
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Does this answer your question? How to add an extra column to a NumPy arrayGreen– Green2019-12-01 11:31:05 +00:00Commented Dec 1, 2019 at 11:31
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4 Answers
You can use the
np.insertnew_x = np.insert(x, 0, 1, axis=1)You can use the
np.appendmethod to add your array at the right of a column of1valuesx = np.array([[1, 2], [3, 4], [5, 6]]) ones = np.array([[1]] * len(x)) new_x = np.append(ones, x, axis=1)
Both will give you the expected result
[[1 1 2]
[1 3 4]
[1 5 6]]
Comments
Try this:
>>> X = np.array([[1, 2], [3, 4], [5, 6]])
>>> X
array([[1, 2],
[3, 4],
[5, 6]])
>>> np.insert(X, 0, 1, axis=1)
array([[1, 1, 2],
[1, 3, 4],
[1, 5, 6]])
answered Dec 1, 2019 at 10:03
Arkistarvh Kltzuonstev
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Comments
Since a new array is going to be created in any event, it is just sometimes easier to do so from the beginning. Since you want a column of 1's at the beginning, then you can use builtin functions and the input arrays existing structure and dtype.
a = np.arange(6).reshape(3,2) # input array
z = np.ones((a.shape[0], 3), dtype=a.dtype) # use the row shape and your desired columns
z[:, 1:] = a # place the old array into the new array
z
array([[1, 0, 1],
[1, 2, 3],
[1, 4, 5]])
Comments
numpy.insert() will do the trick.
X = np.array([[1, 2], [3, 4], [5, 6]])
np.insert(X,0,[1,2,3],axis=1)
The Output will be:
array([[1, 1, 2],
[2, 3, 4],
[3, 5, 6]])
Note that the second argument is the index before which you want to insert. And the axis = 1 indicates that you want to insert as a column without flattening the array.
For reference: numpy.insert()
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