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Given the following text problem statement, write Python code to implement the functionality described below in problem statement
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Problem:
Having a pandas data frame as follow:
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Python Code:
import pandas as pd
df = pd.DataFrame({'a':[12,13,23,22,23,24,30,35,55], 'b':[1,1,1,2,2,2,3,3,3]})
import numpy as np
def g(df):
    return df.groupby("b")["a"].agg([np.mean, np.std])
result = g(df.copy())
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