How to fix IndexError: only integers, slices (`:`), ellipsis (`...`), numpy.newaxis (`None`) and int-CodePudding

I am working on generating a simple sine function defined over the range [0,1] as shown below. However I got an index error when assigning function[i]. I tried to set x_n = int(x_n) as some questions with the same error suggest but that only creates further errors.

import numpy as np

function = np.zeros(20)
x_n=np.arange(0,1,0.05) #[0,1]

for i in x_n:
    function[i] = np.sin(2*np.pi*i)

Note x_n has a step of 0.05 because I need to generate 20 values ranging from 0 to 1.

CodePudding user response：

You don't need to create array zero and insert numbers in this, you can do this with vectorizing magic in NumPy like below:

x_n=np.arange(0,1,0.05) #[0,1]
np.sin(x_n*np.pi*2)

Output:

array([ 0.00000000e 00,  3.09016994e-01,  5.87785252e-01,  8.09016994e-01,
        9.51056516e-01,  1.00000000e 00,  9.51056516e-01,  8.09016994e-01,
        5.87785252e-01,  3.09016994e-01,  1.22464680e-16, -3.09016994e-01,
       -5.87785252e-01, -8.09016994e-01, -9.51056516e-01, -1.00000000e 00,
       -9.51056516e-01, -8.09016994e-01, -5.87785252e-01, -3.09016994e-01])

CodePudding user response：

The problem is that i is a float, while array indices are ints. You should change your code to

import numpy as np

function = np.zeros(20)
x_n=np.arange(0,1,0.05) #[0,1]

for i in x_n:
    function[int(i*20)] = np.sin(2*np.pi*i)

CodePudding user response：

A basic Python iteration tool is enumerate. With this you can iterate on an array of floats, and still get a sequential integer index.

In [16]: arr = np.zeros(20)
    ...: x_n=np.arange(0,1,0.05) #[0,1]
    ...: 
    ...: for i,v in enumerate(x_n):
    ...:     arr[i] = np.sin(2*np.pi*v)
    ...: 
In [17]: arr
Out[17]: 
array([ 0.00000000e 00,  3.09016994e-01,  5.87785252e-01,  8.09016994e-01,
        9.51056516e-01,  1.00000000e 00,  9.51056516e-01,  8.09016994e-01,
        5.87785252e-01,  3.09016994e-01,  1.22464680e-16, -3.09016994e-01,
       -5.87785252e-01, -8.09016994e-01, -9.51056516e-01, -1.00000000e 00,
       -9.51056516e-01, -8.09016994e-01, -5.87785252e-01, -3.09016994e-01])

An alternative is to iterate with for i in range(len(x_n)):, but enumerate is clearer.

But you don't need to iterate (in python) at all:

In [18]: np.sin(2*np.pi*x_n)
Out[18]: 
array([ 0.00000000e 00,  3.09016994e-01,  5.87785252e-01,  8.09016994e-01,
        9.51056516e-01,  1.00000000e 00,  9.51056516e-01,  8.09016994e-01,
        5.87785252e-01,  3.09016994e-01,  1.22464680e-16, -3.09016994e-01,
       -5.87785252e-01, -8.09016994e-01, -9.51056516e-01, -1.00000000e 00,
       -9.51056516e-01, -8.09016994e-01, -5.87785252e-01, -3.09016994e-01])