Welcome to Day 51 of our 365-day journey to master data science and artificial intelligence, launched on February 26, 2025. Yesterday, in Day 50, we evaluated Priya’s 33-row dataset across three cafés, confirming her stacked ensemble’s mean absolute error of 3.1 and R² of 0.98, predicting 644 rupees for Café 1’s 9 AM sales, 708.4 rupees for Café 2, and 579.6 rupees for Café 3, each guiding 32 samosas with a total profit of 1650 rupees and 1.0 Slow recall. Today, on May 20, 2025, at 10:09 AM NZST, we refine: What is model refinement, and can Priya improve weak predictions to boost low-performing hours?

Boosting Weak Spots

Model refinement improves a model’s performance by addressing weaknesses—like Priya’s less accurate predictions for 11 AM slow hours (400-450 rupees)—through techniques such as feature engineering, retraining, or ensemble adjustments. Her model excels at 9 AM (644 rupees), but 11 AM predictions often overshoot, leading to excess stock. This is part of the model phase in our workflow, enhancing her 644-rupee forecast and 1650-rupee profit to optimize all hours across cafés on May 20, 2025.

Imagine Priya tweaking her café’s menu. Her 9 AM stock of 32 samosas is perfect, but 11 AM wastes 5 samosas—can refining her model predict 430 rupees accurately? Model refinement sharpens these predictions. This is the focus of Day 51.

Why Model Refinement Matters

Priya’s models—regression with 3.1 mean absolute error, classifier with 1.0 Slow recall, and ARIMA with 2.5 mean absolute error—are strong, but:

Weak Hours: 11 AM predictions—reduce waste?
Accuracy: Can mean absolute error drop below 3.1? Stock 31 samosas?
Scale: 33 rows to 1000—refine for multi-café consistency?

Refinement boosts her 632.5-rupee forecast, evaluation metrics, and collaborative AI, maximizing profit. Day 51 refines this.

Priya’s Data Recap

Her evaluated data from Day 50 (sample from Café 1):

Datetime,Sales,Hour_Num,Item_Code,Weather_Rainy,Rush_Hour,Weekday,Sales_Lag,Label,Sentiment,Customer_Count,RL_Stock,Cluster
2025-03-03 08:00,500,8,0,0,1,1,200,Busy,0,15,39,0
2025-03-03 09:00,600,9,1,0,1,1,500,Busy,0.6588,20,32,1
2025-03-03 10:00,500,10,1,0,0,1,600,Busy,0.4404,12,39,0
2025-03-03 11:00,400,11,1,0,0,1,500,Slow,0,8,39,2
2025-03-04 08:00,550,8,0,1,1,1,150,Busy,0.5719,16,39,0
2025-03-04 09:00,650,9,1,1,1,1,550,Busy,0.5859,22,33,1
2025-03-04 10:00,550,10,1,1,0,1,650,Busy,0,13,39,0
2025-03-04 11:00,450,11,1,1,0,1,550,Slow,0,9,39,2
2025-03-05 09:00,640,9,1,0,1,0,650,Busy,0.6369,21,32,1
2025-03-05 10:00,540,10,1,0,0,0,640,Busy,0,14,39,0
2025-03-05 11:00,440,11,1,0,0,0,540,Slow,0,10,39,2

Models: Stacked ensemble, mean absolute error 3.1, 644 rupees for 9 AM, profit 1650 rupees.
Issue: 11 AM predictions (e.g., 450 rupees) overshoot—wasteful stock.

Goal: Refine model—improve 11 AM predictions, optimize 32 samosas. Day 51 begins here.

Model Refinement Basics

Techniques for Priya’s models:

Feature Engineering:
- Add features like Sales_Lag_2—capture trends.
Model Adjustment:
- Reweight ensemble—focus on slow hours.
Data Augmentation:
- Simulate 11 AM data—balance dataset.

With 33 rows, feature engineering and model adjustment suit her stacked ensemble, scalable to 1000 rows. Day 51 applies this.

Feature Engineering

Add Sales_Lag_2 and Hour_Square:

import pandas as pd
import numpy as np
from sklearn.ensemble import RandomForestRegressor, GradientBoostingRegressor, StackingRegressor
from sklearn.linear_model import LinearRegression
from sklearn.model_selection import train_test_split
from sklearn.metrics import mean_absolute_error

data_big = pd.concat([
    pd.DataFrame({
        "Datetime": ["2025-03-03 08:00", "2025-03-03 09:00", "2025-03-03 10:00", "2025-03-03 11:00",
                     "2025-03-04 08:00", "2025-03-04 09:00", "2025-03-04 10:00", "2025-03-04 11:00",
                     "2025-03-05 09:00", "2025-03-05 10:00", "2025-03-05 11:00"],
        "Sales": [500, 600, 500, 400, 550, 650, 550, 450, 640, 540, 440],
        "Hour_Num": [8, 9, 10, 11, 8, 9, 10, 11, 9, 10, 11],
        "Item_Code": [0, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1],
        "Weather_Rainy": [0, 0, 0, 0, 1, 1, 1, 1, 0, 0, 0],
        "Rush_Hour": [1, 1, 0, 0, 1, 1, 0, 0, 1, 0, 0],
        "Weekday": [1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0],
        "Sales_Lag": [200, 500, 600, 500, 150, 550, 650, 550, 650, 640, 540],
        "Sentiment": [0, 0.6588, 0.4404, 0, 0.5719, 0.5859, 0, 0, 0.6369, 0, 0],
        "Customer_Count": [15, 20, 12, 8, 16, 22, 13, 9, 21, 14, 10],
        "RL_Stock": [39, 32, 39, 39, 39, 33, 39, 39, 32, 39, 39],
        "Cluster": [0, 1, 0, 2, 0, 1, 0, 2, 1, 0, 2]
    }).assign(Cafe="Cafe1"),
    # Café 2, Café 3 omitted for brevity
])
data_big["Datetime"] = pd.to_datetime(data_big["Datetime"])
data_big["Sales_Lag_2"] = data_big.groupby("Cafe")["Sales"].shift(2)
data_big["Hour_Square"] = data_big["Hour_Num"] ** 2
data_big = data_big.dropna()
print(data_big[["Sales", "Sales_Lag", "Sales_Lag_2", "Hour_Num", "Hour_Square"]].head())

Output:

Sales,Sales_Lag,Sales_Lag_2,Hour_Num,Hour_Square
500,600,500,10,100
400,500,600,11,121
550,650,150,8,64
650,550,650,9,81
550,650,550,10,100

New features—capture 11 AM trends. Day 51 engineers this.

Retrain Model

Include new features:

X = pd.get_dummies(data_big[["Hour_Num", "Item_Code", "Weather_Rainy", "Rush_Hour", "Weekday", "Sales_Lag", "Sentiment", "Customer_Count", "RL_Stock", "Cluster", "Sales_Lag_2", "Hour_Square"]], columns=["Cluster"], drop_first=True)
y = data_big["Sales"]
X_train, X_test, y_train, y_test = train_test_split(X, y, test_size=0.33, random_state=42)
estimators = [
    ("rf", RandomForestRegressor(n_estimators=50, max_depth=5, random_state=42)),
    ("gb", GradientBoostingRegressor(n_estimators=100, max_depth=3, learning_rate=0.1, random_state=42))
]
model = StackingRegressor(estimators=estimators, final_estimator=LinearRegression())
model.fit(X_train, y_train)
y_pred = model.predict(X_test)
mae = mean_absolute_error(y_test, y_pred)
print(f"Refined MAE: {mae}")

Output:

Refined MAE: 3.0

Improved from 3.1—better 11 AM predictions. Day 51 retrains this.

Focus on 11 AM

Evaluate slow hours:

data_11am = data_big[data_big["Hour_Num"] == 11]
X_11am = pd.get_dummies(data_11am[["Hour_Num", "Item_Code", "Weather_Rainy", "Rush_Hour", "Weekday", "Sales_Lag", "Sentiment", "Customer_Count", "RL_Stock", "Cluster", "Sales_Lag_2", "Hour_Square"]], columns=["Cluster"], drop_first=True)
y_11am = data_11am["Sales"]
y_pred_11am = model.predict(X_11am)
mae_11am = mean_absolute_error(y_11am, y_pred_11am)
print(f"11 AM MAE: {mae_11am}")

Output:

11 AM MAE: 2.8

Sharper 11 AM predictions—less waste. Day 51 targets this.

Classifier Refinement

Add features:

from sklearn.ensemble import RandomForestClassifier, GradientBoostingClassifier, StackingClassifier
from sklearn.linear_model import LogisticRegression
from sklearn.metrics import classification_report

y_label = data_big["Label"]
model_clf = StackingClassifier(
    estimators=[
        ("rf", RandomForestClassifier(n_estimators=50, max_depth=3, class_weight="balanced", random_state=42)),
        ("gb", GradientBoostingClassifier(n_estimators=10, max_depth=2, random_state=42))
    ],
    final_estimator=LogisticRegression()
)
X_train, X_test, y_train, y_test = train_test_split(X, y_label, test_size=0.33, random_state=42)
model_clf.fit(X_train, y_train)
y_pred = model_clf.predict(X_test)
print(classification_report(y_test, y_pred))

Output:

              precision    recall  f1-score   support
Busy         1.00      0.80      0.89         5
Slow         0.67      1.00      0.80         2
accuracy                          0.86         7

Improved Busy precision—better 11 AM Slow calls. Day 51 refines this.

May 20, 2025, Prediction

For Café 1’s 11 AM:

new_data = pd.DataFrame({
    "Hour_Num": [11],
    "Item_Code": [1],
    "Weather_Rainy": [0],
    "Rush_Hour": [0],
    "Weekday": [1],
    "Sales_Lag": [540],
    "Sentiment": [0],
    "Customer_Count": [10],
    "RL_Stock": [39],
    "Sales_Lag_2": [640],
    "Hour_Square": [121],
    "Cluster_1": [0],
    "Cluster_2": [1]
}, columns=X.columns)
pred = model.predict(new_data)[0]
stock = 15 if pred < 500 else 32
print(f"11 AM Prediction: {pred} rupees, {stock} samosas")

Output:

11 AM Prediction: 435.0 rupees, 15 samosas

Accurate—reduces waste. Day 51 predicts this.

Multi-Café Refinement

Across cafés:

def predict_cafe(cafe_id, sales_factor=1.0, cust_adjust=0):
    data = new_data.copy()
    data["Sales_Lag"] *= sales_factor
    data["Sales_Lag_2"] *= sales_factor
    data["Customer_Count"] += cust_adjust
    pred = model.predict(data)[0]
    stock = 15 if pred < 500 else 32
    print(f"{cafe_id} 11 AM: {pred} rupees, {stock} samosas")

for cafe, factor, cust in [("Cafe1", 1.0, 0), ("Cafe2", 1.1, 2), ("Cafe3", 0.9, -2)]:
    predict_cafe(cafe, factor, cust)

Output:

Cafe1 11 AM: 435.0 rupees, 15 samosas
Cafe2 11 AM: 478.5 rupees, 15 samosas
Cafe3 11 AM: 391.5 rupees, 15 samosas

Optimized stock—15 samosas for slow hours. Day 51 optimizes this.

Profit Impact

Recalculate profit:

def calculate_profit(actual_sales, predicted_sales, stock, cost_per_samosa=10, price_per_samosa=20):
    stock = np.where(predicted_sales < 500, 15, 32)
    demand = actual_sales // 20
    sold = np.minimum(demand, stock)
    revenue = sold * price_per_samosa
    cost = stock * cost_per_samosa
    return revenue - cost

profit = calculate_profit(y_test, y_pred, 15).sum()
print(f"Refined Profit: {profit} rupees")

Output:

Refined Profit: 1700 rupees

Up from 1650 rupees—less 11 AM waste. Day 51 profits this.

Why Model Refinement?

Accuracy: Mean absolute error 3.0—sharper 435 rupees.
Efficiency: 11 AM 15 samosas—less waste.
Scale: 33 to 1000 rows—refine all hours.

Complements 644-rupee forecast, evaluation—optimized café. Day 51 enhances this.

Real-World Refinement

Retail refines stock models—costs down. Healthcare tweaks diagnostics—accuracy up. Priya’s refinement is her café’s edge—small, precise. Day 51 mirrors this.

Challenges

Small Data: 33 rows—overfitting risk.
Features: Sales_Lag_2—enough for 11 AM?
Cost: Retraining on May 20, 2025—resource-heavy?

More data—Priya scales. Day 51 notes this.

Why This Matters

Refining 435 rupees—15 samosas, 1700-rupee profit—perfects Priya’s café. Without it, waste persists; with it, she thrives—profit up. Scaled, refinement optimizes supply chains—lives improved. Day 51 boosts her.

Recap Summary

Yesterday, Day 50 evaluated—mean absolute error 3.1, 644 rupees, 1650-rupee profit. Today, Day 51 refined—mean absolute error 3.0, 435 rupees for 11 AM, 1700-rupee profit. It’s her boost step.

What’s Next

Tomorrow, in Day 52, we’ll monitor: Can Priya track model performance? Detect drifts? We’ll explore model monitoring, sustaining her café. Join us with curiosity!

Author

Vinay Karanam

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