Pandas - Adding values from DataFrame for different rows

Question

I have a pandas df and I would like to add values for each row from the "total_load" column with the "Battery capacity" column. For example 4755 +(-380) = 4375 and so on. Obviously, what I am doing right now is for every row in the "Battery capacity" column do: 5200 - the value from "total_load" column. Any ideas how I can write that? Should I use an for loop?

 df["Battery capacity"] = 5200 + df["total_load"]

Output should be something like:

time                total_load   battery capacity
2016-06-01 00:00:00   -445        4755
2016-06-01 01:00:00   -380        4375
2016-06-01 02:00:00   -350        4025

Thanks!

What's wrong with how you are doing it now? df["Battery capacity"] = 5200 + df["total_load"] The data in your example appears to be shifted by one row (i.e. 4775 is on the first row and -380 is on the second), so perhaps you want to perform an operation on the shifted data? — Alexander
– Alexander, Commented Aug 15, 2017 at 17:16
Hey Alex, right now I always substract the values from the total_load column with the value "5200". I wanted, as you mentioned, perform the operation on the shifted data. It worked out with .cumsum() as Scott Boston wrote in his answer below! — harald12345
– harald12345, Commented Aug 16, 2017 at 12:36

Scott Boston · Accepted Answer · 2017-08-15 17:17:07Z

2

IIUC, use cumsum to get a "running total" of total_load:

df['Battery capacity'] = df['total_load'].cumsum() + 5200

Output:

                     Battery capacity  total_load
time                                             
2016-01-01 00:00:00            4755.0      -445.0
2016-01-01 01:00:00            4375.0      -380.0
2016-01-01 02:00:00            4025.0      -350.0
2016-01-01 03:00:00            3685.0      -340.0

answered Aug 15, 2017 at 17:17

Scott Boston

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3 Comments

harald12345 Over a year ago

Thanks Scott! Works perfectly. But I have one more question: What if I want to break cumsum once battery capacity is at a certain value? For example if Battery capacity reached 0, I don't want pandas to substract anymore. How could I implement that into this df? For example: df['Battery capacity'] = df['total_load'].cumsum(if battery capacity = 0 then stop substracting) + 5200.

Scott Boston Over a year ago

@harald12345 Look at np.where it as much like an if-then statement. If you start a new question, I am sure myself or someone will answer it quickly.

harald12345 Over a year ago

ok, I will have a luck at np but might also start a new question! cheers

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