Python Lambda Apply Function Multiple Conditions using OR

Question

I've searched this one and cannot find a solution. I have a multiple data condition where when either condition is met, is summed. In my dataset, I have used "apply" and the lambda function for a single condition <, >. However, I have a continuous data column where a count is based on either a low value OR a high value. I have tried variations of this below but keep getting a "ValueError:

ValueError: The truth value of a Series is ambiguous. Use a.empty, a.bool(), a.item(), a.any() or a.all().

Let's say my data looks like this: dfdata

Site   data  month  day   year
A      4     1      1     2021
A      17    1      2     2021
A      8     1      3     2021
A      7     1      1     2022
A      0     1      2     2022
A      2     1      3     2022
B      3     1      1     2021
B      16    1      2     2021
B      9     1      3     2021
B      2     1      1     2022
B      18    1      2     2022
B      5     1      3     2022

I've used a for loop that should give the following result below for evaluating the "data" column and counting the instances of the value < 4 OR > 15. I think that the "|" operator might do this but I get a True/False...

sites = ['A','B']
n = len(sites)
dft = pd.DataFrame(); 
for n in sites: 
    dft.loc[:,n] = dfdata[dfdata['Site']==n].groupby(["month", "day"])["data"].apply(lambda x: (x < 4) or (x > 15).sum())

the result.

month   day   A    B
1       1     0    2
1       2     2    2
1       3     1    0

Thanks for your help.

Code Different · Accepted Answer · 2023-02-04 01:43:50Z

1

You don't have to use (and should avoid) loops in pandas. Aside from being slow, it also make you intention harder to read.

Here's on solution using pandas functions:

dft = (
    dfdata.query("data < 4 or data > 15")
    .groupby(["month", "day", "Site"])["data"]
    .sum()
    .unstack(fill_value=0)
)

The query filters for rows whose data is <4 or >17. The rest is just adding them up and reshaping the resulting dataframe.

answered Feb 4, 2023 at 1:43

Code Different

93.4k16 gold badges154 silver badges175 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

mozway Over a year ago

You might want to use a pivot_table with aggfunc='sum' here ;)

Collectives™ on Stack Overflow

Python Lambda Apply Function Multiple Conditions using OR

1 Answer 1

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related