Python – Reset Increment

I have a list of values in a column (A) and want to increment by 1 in column (B) until the value in A changes, however, having difficulty in my loop to reset the increment when A changes.

B = []
list_length = len(A)

for i in range(0, list_length):
    j = 1
    while A[i] == A[i+1]:
        B = j
        j += 1
        i += 1
    else:
        B = 1
        j += 1

Here is desired output:

Product(A)	No.(B)
Apple	1
Apple	2
Apple	3
Orange	1
Orange	2
Orange	3
Orange	4
Orange	5
Orange	6
Melon	1
Melon	2
Peach	1
Peach	2
Peach	3
Peach	4

Answer

The other two answers are awesome, but I was initially stuck to follow your initial approach with the counter, so here’s what I did:

from prettytable import PrettyTable
 
fruit_table = PrettyTable(["Product(A)", "No.(B)"])

products = ["Apple", "Apple","Apple", "Orange","Orange","Orange","Orange","Orange","Melon","Melon", "Peach","Peach","Peach"]

counter = 0
for i in range(0, len(products)-1):

    if products[i] == products[i+1]:
        counter+= 1
        fruit_table.add_row([products[i],counter])
    else:
        fruit_table.add_row([products[i],counter+1])
        counter=0

print(fruit_table)

Output:

+------------+--------+
| Product(A) | No.(B) |
+------------+--------+
|   Apple    |   1    |
|   Apple    |   2    |
|   Apple    |   3    |
|   Orange   |   1    |
|   Orange   |   2    |
|   Orange   |   3    |
|   Orange   |   4    |
|   Orange   |   5    |
|   Melon    |   1    |
|   Melon    |   2    |
|   Peach    |   1    |
|   Peach    |   2    |
+------------+--------+