How can I prevent the TypeError list indices must be integers not tuple when copying a python list to a numpy array

Question

I am trying to create 3 numpy arrays lists using data from another array called mean data as follows   --- gt  39 R   np array mean data   0        40 P   np array mean data   1        41 Z   np array mean data   2     When I try run the program I get the error   TypeError  list indices must be integers  not tuple   The mean data list looks like this sample      6 0  315 0  4 8123788544375692e-06    6 5  0 0  2 259217450023793e-06    6 5  45 0  9 2823565008402673e-06    6 5  90 0  8 309270169336028e-06    6 5  135 0  6 4709418114245381e-05    6 5  180 0  1 7227922423558414e-05    6 5  225 0  1 2308522579848724e-05    6 5  270 0  2 6905672894824344e-05    6 5  315 0  2 2727114437176048e-05     I don t know how to prevent this error  I have tried creating mean data as a np array and using np append to add values to it but that doesn t solve the problem either   Here s the traceback  was using ipython before   Traceback  most recent call last     File  polarplot py   line 36  in  lt module gt      R   np array mean data   0   TypeError  list indices must be integers  not tuple   And the other way I tried to create an array was   mean data   np array      for ur  ua in it product uradius  uangle       samepoints    data   0   ur   amp   data   1   ua      if samepoints sum    gt  1     check if there is more than one match         np append mean data ur  ua  np mean data samepoints -1         elif samepoints sum      1          np append mean data   ur  ua  data samepoints -1      The traceback on that is   IndexError                                Traceback  most recent call last   lt ipython-input-3-5268bc25e75e gt  in  lt module gt         31     samepoints    data   0   ur   amp   data   1   ua       32     if samepoints sum    gt  1     check if there is more than one match --- gt  33         np append mean data ur  ua  np mean data samepoints -1          34     elif samepoints sum      1       35         np append mean data   ur  ua  data samepoints -1     IndexError  invalid index

User · Answer

You probably do not need to be making lists and appending them to make your array. You can likely just do it all at once, which is faster since you can use numpy to do your loops instead of doing them yourself in pure python.

To answer your question, as others have said, you cannot access a nested list with two indices like you did. You can if you convert mean_data to an array before not after you try to slice it:

R = np.array(mean_data)[:,0]

instead of

R = np.array(mean_data[:,0])

But, assuming mean_data has a shape nx3, instead of

R = np.array(mean_data)[:,0]
P = np.array(mean_data)[:,1]
Z = np.array(mean_data)[:,2]

You can simply do

A = np.array(mean_data).mean(axis=0)

which averages over the 0th axis and returns a length-n array

But to my original point, I will make up some data to try to illustrate how you can do this without building any lists one item at a time:

User · Answer

Just if someone is having this issue and hadn t done list index  sub-index   you could be having the problem because you re missing a comma between two arrays in an array of arrays  It happened to me

User · Answer

The variable mean data is a nested list  in Python accessing a nested list cannot be done by multi-dimensional slicing  i e   mean data 1 2   instead one would write mean data 1  2    This is becausemean data 2  is a list  Further indexing is done recursively - since mean data 2  is a list  mean data 2  0  is the first index of that list    Additionally  mean data    0  does not work because mean data    returns mean data   The solution is to replace the array  or import the original data  as follows   mean data   np array mean data    numpy arrays  like MATLAB arrays and unlike nested lists  support  multi-dimensional slicing with tuples

User · Answer

np append needs the array as the first argument and the list you want to append as the second   mean data   np append mean data   ur  ua  np mean data samepoints -1

User · Answer

import numpy as np  mean data   np array    6 0  315 0  4 8123788544375692e-06    6 5  0 0  2 259217450023793e-06    6 5  45 0  9 2823565008402673e-06    6 5  90 0  8 309270169336028e-06    6 5  135 0  6 4709418114245381e-05    6 5  180 0  1 7227922423558414e-05    6 5  225 0  1 2308522579848724e-05    6 5  270 0  2 6905672894824344e-05    6 5  315 0  2 2727114437176048e-05     R   mean data   0  print R print R shape   EDIT  The reason why you had an invalid index error is the lack of a comma between mean data and the values you wanted to add   Also  np append returns a copy of the array  and does not change the original array  From the documentation       Returns   append   ndarray      A copy of arr with values appended to axis  Note that append does not occur in-place  a new array is allocated and filled  If axis is None  out is a flattened array    So you have to assign the np append result to an array  could be mean data itself  I think   and  since you don t want a flattened array  you must also specify the axis on which you want to append    With that in mind  I think you could try something like  mean data   np append mean data    ur  ua  np mean data samepoints -1      axis 0    Do have a look at the doubled    and      I think they are necessary since both arrays must have the same shape

User · Answer

Seriously this took my much valuable time but not found solution  Basically if you are taking data from sql then you are converting then you can follow these steps  rows   cursor fetchall  ---- only tried on single column dataset    for x in rows      dataset append float x 0

[python] How can I prevent the TypeError: list indices must be integers, not tuple when copying a python list to a numpy array?

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