How to count value change during a for loop in python?

Question

I have a dataframe that consists of one column that consists of 0 and 1 .

They are structured in this way [0,0,1,1,0,0,1,1,1,] .

My goal is to count only the first 1 in each repeating 1 s in a loop.

So in this example of [0,0,1,1,0,0,1,1,1,] it should be able to only count a total of 2 . How can I use a for loop and use an if condition and count this?

Answer 1

(As @Erfan mentiond in the comments :)

>>> df
   col
0    0
1    0
2    1
3    1
4    0
5    0
6    1
7    1
8    1

>>> df['col'].diff().eq(1).sum()
2

Answer 2

Found a messy way to do it where I can create a translated list and count the sum.

def FirstValue(data):      
for index, item in enumerate(data):    
    if item == 1:
        if data[index-1] == 1:
            counter.append(0)            
    if item == 1:
        if data[index-1] == 0:
            counter.append(1)            
    else:
        counter.append(0)

Answer 3

A simple for loop:

out = [0]+[int(j-i==1) for i,j in zip(lst,lst[1:])]

Output:

[0, 0, 1, 0, 0, 0, 1, 0, 0]

Also, you can assign a pd.Series to a DataFrame column like:

df.col = (pd.Series(lst).diff()==1).astype(int)