Cannot change Numpy array's value?

Question

I write a simple code list below:

data = np.array([[1,1,1],[2,3,4]])
xdata = [i + 0.1 for i in data[0]]
print(xdata)
data[0] = xdata
print(data)

But the result I get in console i

[1.1, 1.1, 1.1]
[[1 1 1]
 [2 3 4]]

While I expect it to be

[1.1, 1.1, 1.1]
[[1.1 1.1 1.1]
 [2 3 4]]

Why I can't change the value in NumPy array this way?

I think your problem is similar to this question stackoverflow.com/questions/44500787/… — Python learner
– Python learner, Commented Oct 8, 2021 at 12:01
xdata = [i + 0.1 for i in data[0]] is better written a xdata = data[0]+0.1 — hpaulj
– hpaulj, Commented Oct 8, 2021 at 16:16

Ture Pålsson · Accepted Answer · 2021-10-08 11:59:28Z

2

Create your array like this

data = np.array([[1,1,1],[2,3,4]], type=np.float64)

and it should work. Since you create the array with only integers, its data type becomes np.int64, which means that it can only hold integers.

answered Oct 8, 2021 at 11:59

Ture Pålsson

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Comments

oekopez · Accepted Answer · 2021-10-08 12:01:51Z

1

Your code works mostly as expected with one little problem:

This line

data = np.array([[1,1,1],[2,3,4]])

create a numpy-array of type int, and hence this line

data[0] = xdata

needs to truncate everything behind the decimal point. If you create a float array like this:

data = np.array([[1,1,1],[2,3,4]], dtype=float)

everything will work, as expected. However, if you just want to add to the first row 0.1 a nicer complete solution of your code is:

data = np.array([[1,1,1],[2,3,4]], dtype=float)
data[0] += 0.1

no list comprehension needed.

answered Oct 8, 2021 at 12:01

oekopez

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