210 lines
8.9 KiB
Python
210 lines
8.9 KiB
Python
import numpy as np
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import pandas as pd
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class LogisticRegression:
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'''
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Constructor for the logistic regression with gradient descent. It uses learning rate, iteration number,
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tolerance and verbose. It also initializes the weight, loss, x, y, mean and std.
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'''
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def __init__(self, learning_rate: float, n_iter: int, batch_size: int, tolerance: float, verbose: bool) -> None:
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self.lr = learning_rate
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self.n_iter = n_iter
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self.batch_size = batch_size
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self.tol = tolerance
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self.verbose = verbose
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self.w: np.ndarray | None = None # weight/coefficient (bias as first element)
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self.loss: list[float] = [] # loss per iteration
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self.x: np.ndarray | None = None # matrix of inputs after standardisation
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self.y: np.ndarray | None = None # target vector
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self.mean: np.ndarray | None = None # used for standardisation
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self.std: np.ndarray | None = None # standard deviation
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@staticmethod
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def sigmoid(z: np.ndarray) -> np.ndarray:
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"""Sigmoid method for the logistic regression method."""
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return 1.0 / (1.0 + np.exp(-z)) # 1/(1+exp(-z))
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@staticmethod
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def cost(y: np.ndarray, p: np.ndarray) -> float:
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"""Cross‑entropy loss is used for the cost calculation"""
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eps = 1e-15
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p = np.clip(p, eps, 1 - eps)
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return -np.mean(y * np.log(p) + (1 - y) * np.log(1 - p))
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def prepare(self, df: pd.DataFrame, target_col: str) -> None:
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"""
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Preparation method splits df into x and y. It does define X and Y values from the dataframe and target column.
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Then it does standardisation, adds bias and initializes the weight/coefficient.
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"""
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if target_col not in df.columns:
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raise ValueError(f"Target column '{target_col}' not found in DataFrame.")
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self.y = df[target_col].values.astype(np.int64)
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x_raw = df.drop(columns=[target_col]).values.astype(np.float64)
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# standardisation
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self.mean = x_raw.mean(axis=0)
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self.std = x_raw.std(axis=0)
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self.std[self.std == 0] = 1.0
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x_scaled = (x_raw - self.mean) / self.std # standardisation formula
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bias = np.ones((x_scaled.shape[0], 1), dtype=np.float64) # adding bias
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self.x = np.hstack((bias, x_scaled))
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self.w = np.zeros(self.x.shape[1], dtype=np.float64) # initialize weight as zero
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def fit(self) -> None:
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"""
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Fit method to fit X and Y datas through pandas and train the linear model by gradient descent.
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For the n iterations, it finds probabilities through sigmoid of linear prediction and does the
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gradient to calculate the loss.
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"""
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if self.x is None or self.y is None: # if x or y are empty, throw error
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raise RuntimeError("Model is not fitted yet. Call `prepare` first.")
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n_samples = self.x.shape[0]
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batch_size = self.batch_size or n_samples
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# number of batches per iteration
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n_batches = int(np.ceil(n_samples / batch_size))
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for epoch in range(1, self.n_iter + 1):
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shuffled_idx = np.random.permutation(n_samples) # random permutation of the indices
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for b in range(n_batches):
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start = b * batch_size
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end = min(start + batch_size, n_samples)
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idx = shuffled_idx[start:end]
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x_batch = self.x[idx]
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y_batch = self.y[idx]
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z = x_batch.dot(self.w)
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p = self.sigmoid(z)
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grad = x_batch.T.dot(p - y_batch) / y_batch.size # gradient calculation formula
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self.w -= self.lr * grad # gradient multiplied by learning rate is removed from weight
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# cost is calculated through cross‑entropy and added for the current range
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loss = self.cost(self.y, self.sigmoid(self.x.dot(self.w)))
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self.loss.append(loss)
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# if verbose, it shows the loss every 100 iterations and displays it
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if self.verbose and epoch % 100 == 0:
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print(f"Iter {epoch:4d} – loss: {loss:.6f}")
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# tests whether the absolute change in loss is smaller than the tolerance
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if epoch > 1 and abs(self.loss[-2] - loss) < self.tol:
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if self.verbose:
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print(f"Converged after {epoch} iterations.")
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break
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def predict(self, x: np.ndarray | pd.DataFrame) -> np.ndarray:
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"""
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Predict method is used to test trained data to do Y prediction by multiplying X and weight vectors
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and then calculates the model probability by applying sigmoid function.
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"""
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if isinstance(x, pd.DataFrame): # verifies value type
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x = x.values.astype(np.float64)
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if x.ndim == 1:
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x = x.reshape(1, -1)
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z = x.dot(self.w)
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probs = self.sigmoid(z) # probability calculation through sigmoid method
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return (probs >= 0.5).astype(int) # 0.5 is commonly used to define positivity of the probability
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def score(self, x: np.ndarray | pd.DataFrame, y: np.ndarray | pd.Series) -> float:
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"""
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This method is used to calculate mean accuracy with the prediction of Y and actual Y values.
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"""
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y_pred = self.predict(x)
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y_true = np.asarray(y).astype(int)
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return np.mean(y_pred == y_true) # mean is calculated if Y values match
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if __name__ == "__main__":
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columns = [
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'ID', 'Diagnosis',
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'radius_mean', 'texture_mean', 'perimeter_mean', 'area_mean', 'smoothness_mean',
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'compactness_mean', 'concavitymean', 'concave_points_mean', 'symmetrymean', 'fractal_dimension_mean',
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'radius_se', 'texture_se', 'perimeter_se', 'area_se', 'smoothness_se',
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'compactness_se', 'concavityse', 'concave_points_se', 'symmetryse', 'fractal_dimension_se',
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'radius_worst', 'texture_worst', 'perimeter_worst', 'area_worst', 'smoothness_worst',
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'compactness_worst', 'concavityworst', 'concave_points_worst', 'symmetryworst', 'fractal_dimension_worst'
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]
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df = pd.read_csv('wdbc.data', header=None, names=columns, dtype=str)
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df.drop(columns=['ID'], inplace=True) # drops id column
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missing_rows = df[df.isin(['?', 'NA', 'na', '']).any(axis=1)] # checks null values
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print(f"Rows with null values: {len(missing_rows)}")
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df.replace(['?','NA', 'na', ''], pd.NA, inplace=True) # replace null values with NA identifier
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num_cols = df.columns.difference(['Diagnosis'])
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for col in num_cols:
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df[col] = pd.to_numeric(df[col], errors='coerce') # convert columns to numeric values
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df.dropna(inplace=True) # remove null values
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print(f"Rows remaining after drop of the null values: {len(df)}\n")
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for col in num_cols:
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df = df[df[col] >= 0]
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# sanity checks for data validity - max tumor sizes possible
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df = df[(df['radius_mean'] > 0) & (df['radius_mean'] <= 30)]
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df = df[(df['radius_worst'] > 0) & (df['radius_worst'] <= 30)]
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df = df[(df['texture_mean'] >= 0) & (df['texture_mean'] <= 100)]
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df = df[(df['texture_worst'] >= 0) & (df['texture_worst'] <= 100)]
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df = df[(df['perimeter_mean'] > 0) & (df['perimeter_mean'] <= 200)]
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df = df[(df['perimeter_worst'] > 0) & (df['perimeter_worst'] <= 200)]
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df = df[(df['area_mean'] > 0) & (df['area_mean'] <= 600)]
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df = df[(df['area_worst'] > 0) & (df['area_worst'] <= 600)]
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# check if there are still null values
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assert df.isna().sum().sum() == 0, "There are still some null values."
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# making diagnosis numeric
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df["Diagnosis"] = df["Diagnosis"].map({"M": 1, "B": 0}).astype("category")
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rng = np.random.default_rng(seed=42)
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n_samples = len(df)
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indices = rng.permutation(n_samples)
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train_size = int(0.8 * n_samples)
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train_idx = indices[:train_size]
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test_idx = indices[train_size:]
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df_train = df.iloc[train_idx].reset_index(drop=True)
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df_test = df.iloc[test_idx].reset_index(drop=True)
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# training of the model
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model = LogisticRegression(learning_rate=0.00005, n_iter=5000, batch_size=64, tolerance=1e-6, verbose=True)
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# other values could be used, for example (lr=0.01, n_iter=2000, tolerance=1e-3, verbose=False)
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model.prepare(df_train, target_col="Diagnosis")
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model.fit()
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# evaluation of the model
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train_acc = model.score(model.x, model.y)
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print(f"\nMean accuracy on training data: {train_acc:.4f}")
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# copied prepare method for building test X data
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x_test_raw = df_test.drop(columns=['Diagnosis']).values.astype(np.float64)
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x_test_scaled = (x_test_raw - model.mean) / model.std
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bias_test = np.ones((x_test_scaled.shape[0], 1), dtype=np.float64)
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X_test = np.hstack((bias_test, x_test_scaled))
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y_test = df_test['Diagnosis'].values.astype(int)
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test_acc = model.score(X_test, y_test)
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print(f"Mean accuracy on testing data: {test_acc:.4f}")
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# predict Y values using the trained data
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first_10 = X_test[:10]
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y_hat = model.predict(first_10)
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print("\nFirst 10 predictions:", y_hat.ravel())
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