python machine-learning optimization random-forest particle-swarm

How to build hybrid model of Random Forest and Particle Swarm Optimizer to find optimal discount of products?

I need to find optimal discount for each product (in e.g. A, B, C) so that I can maximize total sales. I have existing Random Forest models for each product that map discount and season to sales. How do I combine these models and feed them to an optimiser to find the optimum discount per product?

Reason for model selection:

RF: it's able to give better(w.r.t linear models) relation between predictors and response(sales_uplift_norm).
PSO: suggested in many white papers (available at researchgate/IEEE), also availability of the package in python here and here.

Input data: sample data used to build model at product level. Glance of the data as below:

Idea/Steps followed by me:

Build RF model per products

 # pre-processed data
 products_pre_processed_data = {key:pre_process_data(df, key) for key, df in df_basepack_dict.items()}
 # rf models
 products_rf_model = {key:rf_fit(df) for key, df in products_pre_processed_data .items()}

Pass the model to optimizer
- Objective function: maximize sales_uplift_norm (the response variable of RF model)
- Constraint:
  - total spend(spends of A + B + C <= 20), spends = total_units_sold_of_products * discount_percentage * mrp_of_products
  - lower bound of products(A, B, C): [0.0, 0.0, 0.0] # discount percentage lower bounds
  - upper bound of products(A, B, C): [0.3, 0.4, 0.4] # discount percentage upper bounds

sudo/sample code # as I am unable to find a way to pass the product_models into optimizer.

from pyswarm import pso
def obj(x):
    model1 = products_rf_model.get('A')
    model2 = products_rf_model.get('B')
    model3 = products_rf_model.get('C')
    return -(model1 + model2 + model3) # -ve sign as to maximize

def con(x):
    x1 = x[0]
    x2 = x[1]
    x3 = x[2]
    return np.sum(units_A*x*mrp_A + units_B*x*mrp_B + units_C* x *spend_C)-20 # spend budget

lb = [0.0, 0.0, 0.0]
ub = [0.3, 0.4, 0.4]

xopt, fopt = pso(obj, lb, ub, f_ieqcons=con)

How to use the PSO optimizer (or any other optimizer if I am not following right one) with RF?

Adding functions used for model:

def pre_process_data(df,product):
    data = df.copy().reset_index()
    # print(data)
    bp = product
    print("----------product: {}----------".format(bp))
    # Pre-processing steps
    print("pre process df.shape {}".format(df.shape))
        #1. Reponse var transformation
    response = data.sales_uplift_norm # already transformed

        #2. predictor numeric var transformation 
    numeric_vars = ['discount_percentage'] # may include mrp, depth
    df_numeric = data[numeric_vars]
    df_norm = df_numeric.apply(lambda x: scale(x), axis = 0) # center and scale

        #3. char fields dummification
    #select category fields
    cat_cols = data.select_dtypes('category').columns
    #select string fields
    str_to_cat_cols = data.drop(['product'], axis = 1).select_dtypes('object').astype('category').columns
    # combine all categorical fields
    all_cat_cols = [*cat_cols,*str_to_cat_cols]
#     print(all_cat_cols)

    #convert cat to dummies
    df_dummies = pd.get_dummies(data[all_cat_cols])

        #4. combine num and char df together
    df_combined = pd.concat([df_dummies.reset_index(drop=True), df_norm.reset_index(drop=True)], axis=1)
    
    df_combined['sales_uplift_norm'] = response
    df_processed = df_combined.copy()
    print("post process df.shape {}".format(df_processed.shape))
#     print("model fields: {}".format(df_processed.columns))
    return(df_processed)


def rf_fit(df, random_state = 12):
    
    train_features = df.drop('sales_uplift_norm', axis = 1)
    train_labels = df['sales_uplift_norm']
    
    # Random Forest Regressor
    rf = RandomForestRegressor(n_estimators = 500,
                               random_state = random_state,
                               bootstrap = True,
                               oob_score=True)
    # RF model
    rf_fit = rf.fit(train_features, train_labels)

    return(rf_fit)

Solution

you can find a complete solution below !

The fundamental differences with your approach are the following :

Since the Random Forest model takes as input the season feature, optimal discounts must be computed for every season.
Inspecting the documentation of pyswarm, the con function yields an output that must comply with con(x) >= 0.0. The correct constraint is therefore 20 - sum(...) and not the other way around. In addition, the units and mrp variable were not given ; I just assumed a value of 1, you might want to change those values.

Additional modifications to your original code include :

Preprocessing and pipeline wrappers of sklearn in order to simplify the preprocessing steps.
Optimal parameters are stored in an output .xlsx file.
The maxiter parameter of the PSO has been set to 5 to speed-up debugging, you might want to set its value to another one (default = 100).

The code is therefore :

import pandas as pd 
from sklearn.pipeline import Pipeline
from sklearn.preprocessing import OneHotEncoder, StandardScaler
from sklearn.compose import ColumnTransformer
from sklearn.ensemble import RandomForestRegressor 
from sklearn.base import clone

# ====================== RF TRAINING ======================
# Preprocessing
def build_sample(season, discount_percentage):
    return pd.DataFrame({
        'season': [season],
        'discount_percentage': [discount_percentage]
    })

columns_to_encode = ["season"]
columns_to_scale = ["discount_percentage"]
encoder = OneHotEncoder()
scaler = StandardScaler()
preproc = ColumnTransformer(
    transformers=[
        ("encoder", Pipeline([("OneHotEncoder", encoder)]), columns_to_encode),
        ("scaler", Pipeline([("StandardScaler", scaler)]), columns_to_scale)
    ]
)

# Model
myRFClassifier = RandomForestRegressor(
    n_estimators = 500,
    random_state = 12,
    bootstrap = True,
    oob_score = True)

pipeline_list = [
    ('preproc', preproc),
    ('clf', myRFClassifier)
]

pipe = Pipeline(pipeline_list)

# Dataset
df_tot = pd.read_excel("so_data.xlsx")
df_dict = {
    product: df_tot[df_tot['product'] == product].drop(columns=['product']) for product in pd.unique(df_tot['product'])
}

# Fit
print("Training ...")
pipe_dict = {
    product: clone(pipe) for product in df_dict.keys()
}

for product, df in df_dict.items():
    X = df.drop(columns=["sales_uplift_norm"])
    y = df["sales_uplift_norm"]
    pipe_dict[product].fit(X,y)

# ====================== OPTIMIZATION ====================== 
from pyswarm import pso
# Parameter of PSO
maxiter = 5

n_product = len(pipe_dict.keys())

# Constraints
budget = 20
units  = [1, 1, 1]
mrp    = [1, 1, 1]

lb = [0.0, 0.0, 0.0]
ub = [0.3, 0.4, 0.4]

# Must always remain >= 0
def con(x):
    s = 0
    for i in range(n_product):
        s += units[i] * mrp[i] * x[i]

    return budget - s

print("Optimization ...")

# Save optimal discounts for every product and every season
df_opti = pd.DataFrame(data=None, columns=df_tot.columns)
for season in pd.unique(df_tot['season']):

    # Objective function to minimize
    def obj(x):
        s = 0
        for i, product in enumerate(pipe_dict.keys()):
            s += pipe_dict[product].predict(build_sample(season, x[i]))
        
        return -s

    # PSO
    xopt, fopt = pso(obj, lb, ub, f_ieqcons=con, maxiter=maxiter)
    print("Season: {}\t xopt: {}".format(season, xopt))

    # Store result
    df_opti = pd.concat([
        df_opti,
        pd.DataFrame({
            'product': list(pipe_dict.keys()),
            'season': [season] * n_product,
            'discount_percentage': xopt,
            'sales_uplift_norm': [
                pipe_dict[product].predict(build_sample(season, xopt[i]))[0] for i, product in enumerate(pipe_dict.keys())
            ]
        })
    ])

# Save result
df_opti = df_opti.reset_index().drop(columns=['index'])
df_opti.to_excel("so_result.xlsx")
print("Summary")
print(df_opti)

It gives :

Training ...
Optimization ...
Stopping search: maximum iterations reached --> 5
Season: summer   xopt: [0.1941521  0.11233673 0.36548761]
Stopping search: maximum iterations reached --> 5
Season: winter   xopt: [0.18670604 0.37829516 0.21857777]
Stopping search: maximum iterations reached --> 5
Season: monsoon  xopt: [0.14898102 0.39847885 0.18889792]
Summary
  product   season  discount_percentage  sales_uplift_norm
0       A   summer             0.194152           0.175973
1       B   summer             0.112337           0.229735
2       C   summer             0.365488           0.374510
3       A   winter             0.186706          -0.028205
4       B   winter             0.378295           0.266675
5       C   winter             0.218578           0.146012
6       A  monsoon             0.148981           0.199073
7       B  monsoon             0.398479           0.307632
8       C  monsoon             0.188898           0.210134