Cannot get groupby records based on their minimum value using pandas in python

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粉色の甜心
粉色の甜心 2021-01-23 00:15

I have the following csv

id;price;editor
k1;10,00;ed1
k1;8,00;ed2
k3;10,00;ed1
k3;11,00;ed2
k2;10,50;ed1
k1;9,50;ed3

If I do the following

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5条回答
  • 2021-01-23 00:33

    Group the data by only id and find min price for each group. Index the original dataframe based on the minimum values to include the editor column.

    Note: I am assuming that the comma in price column is a typo

    df.loc[df['price'] == df.groupby('id')['price'].transform('min')]
    
    
        id  price   editor
    1   k1  8.0     ed2 
    2   k3  10.0    ed1 
    4   k2  10.5    ed1 
    
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  • 2021-01-23 00:38

    get rid of the editor part:

    df_reduced= df.groupby(['id'])['price'].min()
    

    no need to include 'transformed' as somebody else stated

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  • 2021-01-23 00:46

    Much like @Wen-Ben I choose to use sort_values and drop_duplicates, however, I converted the values using pd.read_csv with the decimal parameter.

    from io import StringIO
    
    csvfile = StringIO("""id;price;editor
    k1;10,00;ed1
    k1;8,00;ed2
    k3;10,00;ed1
    k3;11,00;ed2
    k2;10,50;ed1
    k1;9,50;ed3""")
    
    df = pd.read_csv(csvfile, delimiter =';', decimal=',')
    
    df.sort_values(['id','price']).drop_duplicates(['id']) 
    

    Output:

       id  price editor
    1  k1    8.0    ed2
    4  k2   10.5    ed1
    2  k3   10.0    ed1
    
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  • 2021-01-23 00:54

    drop_duplicate + sort_values

    #df['price'] = pd.to_numeric(df['price'].str.replace(",", "."))
    
    df.sort_values('price').drop_duplicates(['id'])
    Out[423]: 
       id  price editor
    1  k1    8.0    ed2
    2  k3   10.0    ed1
    4  k2   10.5    ed1
    
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  • 2021-01-23 00:54

    The instruction

    df_reduced= df.groupby(['id', 'editor'])['price'].min()
    

    will give you the min price per each unique id-editor pair, you want the min per id. However, since your price field has a string format, you first need to cast it to numeric in order to run the groupby:

    df['price'] = pd.to_numeric(df1['price'].str.replace(",", "."))
    df.loc[df.groupby('id')['price'].idxmin()]
    

    Output

       id  price editor
    1  k1    8.0    ed2
    4  k2   10.5    ed1
    2  k3   10.0    ed1
    
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