Changing a value in an array

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  • Thread starter ver_mathstats
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In summary: That's because they can easily be mistaken for function parameters.def array_change(arr, new_val): arr_size = len(arr) for i in range(arr_size): arr[i], new_val = arr[i], new_valdef array_change(arr, new_val): arr_size = len(arr) for i in range(arr_size, 0, -1): arr[i], new_val = arr[i], new_valdef array_change(arr, new_val):
  • #1
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Homework Statement
Write a Python code to create the function array_change(a, new_val) that has two arguments:
a that is a NumPy array whose entries are numbers, and
new_val which is a number. The function returns a new array after changing every occurrence of entries in
a, that are in absolute value strictly less than 1, to new_val.
Relevant Equations
Python
Code:
import numpy as np

def array_change(a,new_val):
    a=np.array([])
    for i in range(a):
        if abs(i)<1:
            a[i]=new_val

e=np.arange(-2, 2, 0.2).reshape(4,5)
print(array_change(e,0))

I am not sure where I am going wrong exactly but I keep getting an error message.
I came up with a code that gives me the results I am looking for but it is not a function.

Code:
e=np.arange(-2, 2, 0.2).reshape(4,5)
c=abs(e)<1
e[c]=0
print(e)

Any help is appreciated. Thank you.
 
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  • #2
What does the error message say? That might give you a hint. That is what they are for.
 
  • #3
You have some code that works. Can you figure a way to put that into a function? Remember that a function usually returns a value.
 
  • #4
ver_mathstats said:
I am not sure where I am going wrong exactly but I keep getting an error message.
If your code produces an error message, it's always a good idea to tell anyone helping what that error message says. A typical Python error message will give the type of error (e.g., Syntax Error, or Name Error) and will show you what line the error occurs on.
 
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  • #5
Aside from the program requirements (one parameter of the function must be a Numpy array), I don't see any other real reason why an ordinary Python list type can't be used.
 
  • #6
I see at least two things wrong:

(1) a is the input array, which comes from outside the function. You should not be re-defining a within the function.

(2) The statement "for i in range(a)" requires that a be an integer. But a is a numpy array, not an integer. So this will fail right away.

Try fixing these two things and thinking a bit more about what you are trying to do. Then come back and tell us how you are doing.
 
  • #7
To elaborate on the points that @phyzguy made, instead of doing this:
Python:
def array_change(a,new_val):
    a=np.array([])
      for i in range(a):
try this:
Python:
def array_change(arr, new_val):  
    arr_size = len(arr)
    for i in range(arr_size):
Note that I changed the name of the array parameter. Single letter variable names are discouraged in most programming languages, except possibly for loop control variables such as i, j, k, and so on.
 

1. How do I change a specific value in an array?

To change a specific value in an array, you can use the index of the value you want to change and the assignment operator (=) to assign a new value to that index.

2. Can I change multiple values in an array at once?

Yes, you can use a loop or a built-in method such as map() or forEach() to change multiple values in an array at once.

3. What happens if I try to change a value in an array that doesn't exist?

If you try to change a value in an array that doesn't exist, the value will be added to the end of the array.

4. How can I check if a value in an array has been successfully changed?

You can use the console.log() method to print the array and check if the value has been changed. Alternatively, you can use the includes() method to check if the array contains the new value.

5. Is it possible to change the data type of a value in an array?

Yes, you can change the data type of a value in an array by assigning a new value with a different data type to that index. However, it is important to note that this may cause unexpected behavior and should be done carefully.

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