[FEA] Series and DataFrame idxmax and idxmin

[beckernick]

For API compatibility, cuDF should support idxmax and idxmin on Series and DataFrames.

Note that argmin and argmax (https://github.com/rapidsai/cudf/issues/9601) are slightly different from idxmin and idxmax. The latter methods return the index label associated with the first occurrence of the minimum or maximum value. The index label may not be an integer (see example below).

On DataFrmes, these methods return a Series in which each row corresponds to one column in the original dataFrame.

import pandas as pd
​
df = pd.DataFrame({'consumption': [10.51, 103.11, 55.48],
                   'co2_emissions': [37.2, 19.66, 1712]},
                   index=['Pork', 'Wheat Products', 'Beef'])
print(df, "\n")
print(df.idxmax(), "\n")
print(df.idxmin())
                consumption  co2_emissions
Pork                  10.51          37.20
Wheat Products       103.11          19.66
Beef                  55.48        1712.00 

consumption      Wheat Products
co2_emissions              Beef
dtype: object 

consumption                Pork
co2_emissions    Wheat Products
dtype: object

import pandas as pd
​
df = pd.DataFrame({'consumption': [10.51, 103.11, 55.48],
                   'co2_emissions': [37.2, 19.66, 1712]})
print(df, "\n")
print(df.idxmax(), "\n")
print(df.idxmin())
   consumption  co2_emissions
0        10.51          37.20
1       103.11          19.66
2        55.48        1712.00 

consumption      1
co2_emissions    2
dtype: int64 

consumption      0
co2_emissions    1
dtype: int64

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[espackman-nv]

Hi all, I just attempted to use idxmin with my CUDF dataframe which resulted in an AttributeError: DataFrame object has no attribute idxmin. I was able to reproduce the error using the above Argentinian consumption DF. Any idea on work arounds?