CODEWITHSUNDEEP
pythonarraysnumpymultidimensional-array
alx
alx

Reputation: 844

How to create 2d NumPy array with for loop [Python]

Get a problem There is a double cycle, on the secondary loop we get an array of 10 elements. Then, after each cycle (first), you need to add these elements to the array. At the output, you need to get an array of the form:

result_array = [[inter2d_resultFIRST],[inter2d_resultSECOND],[inter2d_resultTHIRD]]

CODE: 

points = np.array([[-100, 0], [100, 0], [100, 300],[-100,300]])
density = 1000 
result_array = np.array([])
visual_x = np.array([])

for h in range(3):
    points = np.array([[-100, 0], [100, 0], [100, 300],[-100,300]])
    inter_result = np.array([])
    inter2d_result = np.array([])
    poly = [mesher.Polygon(points,{'density': density})]
    xp = np.arange(-10000, 10000, 10.0)
    zp = np.zeros_like(xp)
    for i in range(10):
        poly = [mesher.Polygon(points,{'density': density})]
        xp = np.arange(-10000, 10000, 10.0)
        zp = np.zeros_like(xp)
        gz = talwani.gz(xp, zp, poly)
        inter_result = np.append(inter_result, np.nanmax(gz))
        visual_x = np.append(visual_x, points[1][0]*2)
        points[0][0] = points[0][0] - 10
        points[1][0] = points[1][0] + 10
        points[2][0] = points[2][0] + 10
        points[3][0] = points[3][0] - 10
    inter2d_result = np.append(inter2d_result,inter_result)
    result_array = np.append(result_array[h], inter2d_result)

Get the error:

IndexError                                Traceback (most recent call last)
<ipython-input-87-c3ef6fe1381b> in <module>()
     40 
     41     inter2d_result = np.append(inter2d_result,inter_result)
---> 42     result_array = np.append(result_array[h], inter2d_result)
     43 
     44 

IndexError: index 0 is out of bounds for axis 0 with size 0

Upvotes: 0

Views: 3291

Answers (2)

DrM
DrM

Reputation: 2515

First lets focus on the append operation,

import numpy as np
a = np.array( [1,2,3] )
b = np.array( [4,5,6] )

np.append( a, b )

produces

array( [1, 2, 3, 4, 5, 6] )

What you might want is 

np.append( [a], [b], 0 )

which produces

array([ [1, 2, 3], [4, 5, 6] ])

Note that here a 0 appears in the third parameter to specify the axis for the append operation.

Regarding the error, the index h, tells numpy to append to the 'h'-th element. That's probably not what you intended. Also, the index is not correct since 'h' is always one more than the number of elements in the array at the point where the call occurs.

Upvotes: 2

glycoaddict
glycoaddict

Reputation: 929

I think you're trying to append a value to result_array. You should try without the (h) because what that will do is try to index the value already existing in result_array at index h. But since the array is empty to start so there is no 0th value, and h=0 for the first iteration, so that's why you're getting the error.

Maybe try np.append(result_array, inter2d_result)

Upvotes: 0

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