Change values in a list of numpy arrays

Question

I have a list of numpy arrays

nplist =  [(array([[2.50000000e+01, 4.09600003e+03, 4.33334732e+00],
           [2.50000000e+01, 1.36533336e+03, 7.00000381e+00],
           [1.50000000e+01, 1.22880000e+04, 1.00002670e+00],
           [1.50000000e+01, 2.59413333e+04, 3.33362579e-01],
           [2.50000000e+01, 2.86734757e+04, 4.16426142e+00],
           [2.00000000e+01, 5.99947347e+03, 2.27296132e+00]]), array([[-0.65173667],
           [-0.65174361],
           [-0.63682517],
           [-0.65175054],
           [-0.64986406],
           [-0.64614659]]))]

How can I set the second array negative? If I write nplist[0][1] I get

array([[-0.65173667],
       [-0.65174361],
       [-0.63682517],
       [-0.65175054],
       [-0.64986406],
       [-0.64614659]])

So why I can't do nplist[0][1] = -nplist[0][1] Then I get

Traceback (most recent call last):
  File "/snap/pycharm-professional/167/helpers/pydev/_pydevd_bundle/pydevd_exec2.py", line 3, in Exec
    exec(exp, global_vars, local_vars)
  File "<input>", line 1, in <module>
TypeError: 'tuple' object does not support item assignment

It's already negative

U13-Forward
– U13-Forward

2019-11-05 07:32:57 +00:00
Commented Nov 5, 2019 at 7:32 — U13-Forward
– U13-Forward, Commented Nov 5, 2019 at 7:32
You mean positive?

U13-Forward
– U13-Forward

2019-11-05 07:33:13 +00:00
Commented Nov 5, 2019 at 7:33 — U13-Forward
– U13-Forward, Commented Nov 5, 2019 at 7:33

Chris · Accepted Answer · 2019-11-05 07:35:49Z

1

Its because tuple is an immutable. Change it into list beforehand:

nplist[0] = list(nplist[0])
nplist[0][1] = -nplist[0][1] 
nplist[0][1]

Output:

array([[0.65173667],
       [0.65174361],
       [0.63682517],
       [0.65175054],
       [0.64986406],
       [0.64614659]])

answered Nov 5, 2019 at 7:35

Chris

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