Pandas groupby and apply function on group-CodePudding

On a pandas df of the below info

STOCK    YR    MONTH  DAY     PRICE
AAA     2022    1     1        10
AAA     2022    1     2        11
AAA     2022    1     3        10
AAA     2022    1     4        15
AAA     2022    1     5        10
BBB     2022    1     1        5
BBB     2022    1     2        10
BBB     2022    2     1        10
BBB     2022    2     2        15

I am trying to group by STOCK and applying the following function

def next_pred(currents):
    model = SimpleExpSmoothing(currents['PRICE'])
    model_fit=model.fit()
    next_price=model_fit.predict()     
    return (int(np.floor(next_price)))

I am using the following line of code:

future_price =df.groupby(['STOCK']).apply(lambda x: next_pred(x)).reset_index()

However, I am getting the below error:

IndexError: too many indices for array: array is 0-dimensional, but 1 were indexed

A print of the df['PRICE'] from within the function, prints the data properly. Any suggestions on what might be causing the indexing error? Thanks! But I am not sure

CodePudding user response：

With the current sample data, no error. To reproduce the error, add this row for example

df.loc[9] = ['CCC',2022,1,1,30]

then the error is related to groups that have only one row. One way is then to remove these 1-row groups using duplicated like:

res = (
    df[df['STOCK'].duplicated(keep=False)]
      .groupby(['STOCK']).apply(lambda x: next_pred(x))
      .reset_index()
)