Python pandas 如何将累积计数器添加到相邻列？

Question

I have a csv file with something like this column

Comulative
-1
-3
-4
1
2
5
-1
-4
-8
1
3
5
10

I would like to add an internal column counting the number of sign shifts

To get something like this

Comulative	Score
-1	1
-3	2
-4	3
1	1
2	2
5	3
-1	1
-4	2
-8	3
1	1
3	2
5	3
10	4

In my original csv file, the Comulative column usually does not change the sign from about 100 to 500 lines here, for clarity, it changes so often !

Can you tell me how to do it better?

Answer 1

Get the sign with numpy.sign , then use a custom groupby with cumcount :

# get sign
s = np.sign(df['Comulative'])
# group by consecutive signs
group = s.ne(s.shift()).cumsum()
# enumerate
df['Score'] = s.groupby(group).cumcount().add(1)

NB. if you want to consider 0 as part of the positive numbers, use s = df['Comulative'].gt(0) .

output:

    Comulative  Score
0           -1      1
1           -3      2
2           -4      3
3            1      1
4            2      2
5            5      3
6           -1      1
7           -4      2
8           -8      3
9            1      1
10           3      2
11           5      3
12          10      4

Answer 2

mozway's usage of np.sign is far prettier, but for a more drawn out answer - you could do something like this.

# Marks true every time the previous value is positive, 
# and the current is negative or visa versa.
groups = (df.Comulative.lt(0) & df.Comulative.shift().gt(0) 
         | df.Comulative.gt(0) & df.Comulative.shift().lt(0)).cumsum()

df['Score'] = df.groupby(groups).cumcount().add(1)

Output:

    Comulative  Score
0           -1      1
1           -3      2
2           -4      3
3            1      1
4            2      2
5            5      3
6           -1      1
7           -4      2
8           -8      3
9            1      1
10           3      2
11           5      3
12          10      4