I am using GridSearchCV for optimising my predictions

I am running a fairly large dataset and I am afraid I have not optimised the parameters enough.

         Unnamed: 0           col1           col2           col3           col4          col5
count  8.886500e+05  888650.000000  888650.000000  888650.000000  888650.000000  888650.000000
mean   5.130409e+05       2.636784       3.845549       4.105381       1.554918       1.221922
std    2.998785e+05       2.296243       1.366518       3.285802       1.375791       1.233717
min    4.000000e+00       1.010000       1.010000       1.010000       0.000000       0.000000
25%    2.484332e+05       1.660000       3.230000       2.390000       1.000000       0.000000
50%    5.233705e+05       2.110000       3.480000       3.210000       1.000000       1.000000
75%    7.692788e+05       2.740000       3.950000       4.670000       2.000000       2.000000
max    1.097490e+06      90.580000      43.420000      99.250000      22.000000      24.000000

         Unnamed: 0      col1        col2        col3        col4        col5
count  390.000000  390.000000  390.000000  390.000000         0.0         0.0
mean   194.500000    3.393359    4.016821    3.761385         NaN         NaN
std    112.727548    4.504227    1.720292    3.479109         NaN         NaN
min      0.000000    1.020000    2.320000    1.020000         NaN         NaN
25%     97.250000    1.792500    3.272500    2.220000         NaN         NaN
50%    194.500000    2.270000    3.555000    3.055000         NaN         NaN
75%    291.750000    3.172500    4.060000    4.217500         NaN         NaN
max    389.000000   50.000000   18.200000   51.000000         NaN         NaN

The way I am using GridSearchCV is as follows:

rf_h = RandomForestRegressor()
rf_a = RandomForestRegressor()

# Using GridSearch for Optimisation
param_grid = {
'max_features': ['auto', 'sqrt', 'log2']

rf_g_h = GridSearchCV(estimator=rf_h, param_grid=param_grid, cv=3, n_jobs=-1)
rf_g_a = GridSearchCV(estimator=rf_a, param_grid=param_grid, cv=3, n_jobs=-1)

# Fitting dataframe to prediction engine
rf_g_h.fit(X_h, y_h)
rf_g_a.fit(X_a, y_a)

How can I optimise param_grid and hence determine best_params_ of the same?

What would be the best matrix for n_estimators for this dataset?


2 Answers 2


In general there's no way to know the best values to try for a parameter. The only thing one can do is to try many possible values, but:

  • this mathematically requires more computing time (see this question about how GridSearchCV works)
  • there is a risk of overfitting the parameters, i.e. selecting a value which is optimal by chance on the validation set.
  • $\begingroup$ This is exactly what I wanted to see and understand.. I am a python noob but a soccer fan.. i wanted to build a prediction.. and have built one.. lol.. too much detail but I wanna say Thank You this will help me build a better model.. so beautifully written.. used discts on my code but when i saw your response, i unserstoos what a disc is actually is... so yeah thank you. but i cannot accept it as answer because it is not and WANT the best params.. $\endgroup$
    – PyNoob
    Jul 16, 2021 at 14:55
  • $\begingroup$ Again.. sorry.. not being rude.. but just being excited.. will wait for 7 more days, if completed, will mark yours as best answer. sorry sis not mean to come out rude.. but so goos answer.. thank you. Edit.. meant to say dict $\endgroup$
    – PyNoob
    Jul 16, 2021 at 14:56
  • $\begingroup$ Also, what is max_features': ['auto', 'sqrt', 'log2'] in my code.. what are the various options there? How do they work..? I can understand its a lot asking but i wanna predict soccer matches.. and i want to have the best combinations possible in a classifier so I have to know what goes in there and it works per se.. RandomForestRegressor engine.. so i am not going in more detail.. $\endgroup$
    – PyNoob
    Jul 16, 2021 at 15:05
  • $\begingroup$ I am sorry, i am being verbose, possibly wrong place to ask to get in touch but I want to ask and any other place or email or github, page and all, there are chat forums but it would be an overkill, if you would like, i can ask a similar question on your page and continue to reply. $\endgroup$
    – PyNoob
    Jul 16, 2021 at 15:08
  • $\begingroup$ @PyNoob technically the default gridsearch is a brute-force algorithm, it just tries every possible value. The randomized version can be a good option in case you want to try many values. A more manual approach is to plot the performance for some values for a single parameter, for instance n=50,100,150... then by observing how the curve evolves based on the values it gives you a more precise idea of which range of values is optimal. you can do that iteratively, but it takes time of course. $\endgroup$
    – Erwan
    Jul 16, 2021 at 20:10

Instead of GridSearchCV you should try Optuna. It is much faster than GridSearchCV.

But apart from that, coming to your question, there is no best value for a hyperparameter per se! Period! It depends on what kind of data you have. What hyperparameter value works for one dataset might not work for another dataset.

Also another point to keep in mind, there are many parameters for a model like Random Forest model. Including all of them with a wide range of values in your gridsearch will take forever. Instead include only those parameters that give the maximum improvement in your results (aka those that matter the most!). Here is a link to a blog that might help you: https://blog.dataiku.com/narrowing-the-search-which-hyperparameters-really-matter

Hope it helps!

  • $\begingroup$ HO can I call and use optuna? Can I just replace GridSearchCV with optuna? $\endgroup$
    – PyNoob
    Jul 20, 2021 at 1:30
  • $\begingroup$ Edit: correction- How* $\endgroup$
    – PyNoob
    Jul 20, 2021 at 1:36
  • $\begingroup$ Here is an excellent article about the implementation of optuna: analyticsvidhya.com/blog/2020/11/… If you found my answer useful kindly mark it as best! Happy Coding! $\endgroup$
    – spectre
    Jul 20, 2021 at 4:43

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