Is there a query method or similar for pandas Series (pandas.Series.query())?

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终归单人心
终归单人心 2021-02-18 20:02

The pandas.DataFrame.query() method is of great usage for (pre/post)-filtering data when loading or plotting. It comes particularly handy for method chaining.

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  • 2021-02-18 20:27

    Instead of query you can use pipe:

    s.pipe(lambda x: x[x>0]).pipe(lambda x: x[x<10])
    
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  • 2021-02-18 20:29

    IIUC you can add query("Points > 100"):

    df = pd.DataFrame({'Points':[50,20,38,90,0, np.Inf],
                       'Player':['a','a','a','s','s','s']})
    
    print (df)
      Player     Points
    0      a  50.000000
    1      a  20.000000
    2      a  38.000000
    3      s  90.000000
    4      s   0.000000
    5      s        inf
    
    points_series = df.query("Points < inf").groupby("Player").agg({"Points": "sum"})['Points']
    print (points_series)     
    a = points_series[points_series > 100]
    print (a)     
    Player
    a    108.0
    Name: Points, dtype: float64
    
    
    points_series = df.query("Points < inf")
                      .groupby("Player")
                      .agg({"Points": "sum"})
                      .query("Points > 100")
    
    print (points_series)     
            Points
    Player        
    a        108.0
    

    Another solution is Selection By Callable:

    points_series = df.query("Points < inf")
                      .groupby("Player")
                      .agg({"Points": "sum"})['Points']
                      .loc[lambda x: x > 100]
    
    print (points_series)     
    Player
    a    108.0
    Name: Points, dtype: float64
    

    Edited answer by edited question:

    np.random.seed(1234)
    df = pd.DataFrame({
        'Points': [np.random.choice([1,3]) for x in range(100)], 
        'Player': [np.random.choice(["A","B","C"]) for x in range(100)]})
    
    print (df.query("Points == 3").Player.value_counts().loc[lambda x: x > 15])
    C    19
    B    16
    Name: Player, dtype: int64
    
    print (df.query("Points == 3").groupby("Player").size().loc[lambda x: x > 15])
    Player
    B    16
    C    19
    dtype: int64
    
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  • 2021-02-18 20:39

    Why not convert from Series to DataFrame, do the querying, and then convert back.

    df["Points"] = df["Points"].to_frame().query('Points > 100')["Points"]
    

    Here, .to_frame() converts to DataFrame, while the trailing ["Points"] converts to Series.

    The method .query() can then be used consistently whether or not the Pandas object has 1 or more columns.

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