I'm trying to delete some elements from array this way:
a = [2, 5, 10, 20, 30, 40]
for i in range(len(a)):
print(a[i], i)
if (a[i] > 20):
a = np.delete(a, i)
print(a)
And I catch an error: index 5 is out of bounds for axis 0 with size 5. I don't really understand what's wrong with the code above. Could somebody, please, explain the problem?
In this list: [1,2,3]
When the second element is deleted, you get: [1,3]
When traversing the list left-to-right, removing elements changes the index of the rest of the list. So, when you want to remove the 3, you must remove the second element, not the third.
Solution: traverse the list right-to-left.
You are applying numpy operations on regular list, also still if you use .pop(), you will delete items while iterating list, so use another list and assign slice copy of it:
a = [2, 5, 10, 20, 30, 40]
n = []
for i in range(len(a)):
print(a[i], i)
if (a[i] < 20):
n.append(a[i])
a = n[:]
print(a)
List length varies by removing elements. You need to track the original list in loop. In the following sample I kept the original elements of the list and applied the change in a copied one.
a = [2, 5, 10, 20, 30, 40]
b = a[:]
for i in a:
if (i > 20):
b.remove(i)
print(b)
so, you deleted the [30] element from the list, your list the last index will be 4, then you will access a[5] -> error!
a = [2, 5, 10, 20, 30, 40]
a2 = []
for i in a:
print(i)
if (i <= 20):
a2.append(i)
print(a2)
output
2
5
10
20
30
40
[2, 5, 10, 20]
aas it changes in the loop? You printa[i]but nota.