I have an array that looks like (simplified version):
[14 14 14 14 14 13 13 13 13 13 2 2 2 2 2 2 2 2 2]
What I need to do is to identify the index where it changes. Like index 5 is 13 and so on. I do not know how to do this. Any kind of help is welcomed!! :)
I've tried it with np.unique, but the output of this sorts the numbers ascending, so I lose where the numbers actually change.
Pythonic way, using a list comprehension:
arr=[15,14,14,14,14,14,13,13,13,13,13,2,2,2,2,2,2,2,2,2,3]
[i+1 for i in range(len(arr)-1) if arr[i] != arr[i+1]]
# >>> [1, 6, 11, 20]
You can compare each item in the array with the next item using a[1:]!=a[:-1] (for some 1d array a). You can then convert this array of booleans to indices by using np.where. Because of the slicing, you need to add one to this.
# added a 4 to the end of the array to have an extra place where the number changes
a=np.array([14, 14, 14, 14, 14, 13, 13, 13, 13, 13, 2, 2, 2, 2, 2, 2, 2, 2, 2,4])
changes = np.where(a[1:]!=a[:-1])[0]+1
print('change indices:',changes)
print('before each change:',a[changes-1])
print('after each change:',a[changes])
This outputs:
change indices: [ 5 10 19]
before each change: [14 13 2]
after each change: [13 2 4]
This is fastest way possible to find the unique number index change.
import numpy as np
arr = np.array([14, 14, 14, 13, 20, 20, 20, 2, 2, 2])
np.unique(arr, return_index=True)
(array([ 2, 13, 14, 20]), array([7, 3, 0, 4]))
Check out this code :
arr = [14,14,14,14,14,13,13,13,13,13,2,2,2,2,2,2,2,2,2]
k = arr[0]
for i, j in enumerate(arr):
if k != j:
print(i)
k = arr[i]
OUTPUT:
5
10
It very simple use a loop
all_indexes = []
lisst = [14,14, 14, 14, 14, 13, 13, 13, 13, 13, 2, 2 ,2, 2, 2, 2, 2, 2, 2]
for i in range(len(lisst)-1):
if lisst[i] != lisst[i+1]:
all_indexes.append(i+1)
print(all_indexes)
