机器学习 (ML) 是科技行业最受欢迎的领域之一，鉴于其丰富的库和易用性，熟练掌握 Python 通常是先决条件。如果您正在准备该领域的面试，那么精通理论概念和实际实现至关重要。以下是一些常见的 Python ML 面试问题和答案，可帮助您做好准备。
预处理技术对于为机器学习模型准备数据至关重要。一些最常见的技术包括：
from sklearn.preprocessing import MinMaxScaler import pandas as pd # Data normalization scaler = MinMaxScaler() normalized_data = scaler.fit_transform(data) # Creating dummy variables df_with_dummies = pd.get_dummies(data, drop_first=True)
暴力算法彻底尝试所有可能性来找到解决方案。一个常见的例子是线性搜索，其中算法检查数组的每个元素以查找匹配项。
def linear_search(arr, target):
for i in range(len(arr)):
if arr[i] == target:
return i
return -1
# Example usage
arr = [2, 3, 4, 10, 40]
target = 10
result = linear_search(arr, target)
不平衡的数据集类别比例存在偏差。处理此问题的策略包括：
from imblearn.over_sampling import SMOTE from sklearn.model_selection import train_test_split X_resampled, y_resampled = SMOTE().fit_resample(X, y) X_train, X_test, y_train, y_test = train_test_split(X_resampled, y_resampled, test_size=0.2)
处理缺失数据的常见策略包括省略和插补：
from sklearn.impute import SimpleImputer # Imputing missing values imputer = SimpleImputer(strategy='median') data_imputed = imputer.fit_transform(data)
回归是一种监督学习技术，用于查找变量之间的相关性并对因变量进行预测。常见的例子包括线性回归和逻辑回归，可以使用 Scikit-learn 来实现。
from sklearn.linear_model import LinearRegression from sklearn.model_selection import train_test_split # Split the dataset X_train, X_test, y_train, y_test = train_test_split(X, y, test_size=0.2) # Create and train the model model = LinearRegression() model.fit(X_train, y_train) # Make predictions predictions = model.predict(X_test)
在 Python 中，您可以使用 Scikit-learn 中的 train_test_split 函数将数据拆分为训练集和测试集。
from sklearn.model_selection import train_test_split # Split the dataset: 60% training and 40% testing X_train, X_test, y_train, y_test = train_test_split(data.data, data.target, test_size=0.4)
基于树的学习器的一些关键参数包括：
from sklearn.ensemble import RandomForestClassifier # Setting parameters for Random Forest model = RandomForestClassifier(max_depth=5, n_estimators=100, max_features='sqrt', random_state=42) model.fit(X_train, y_train)
两种常用的超参数调整方法是：
from sklearn.model_selection import GridSearchCV, RandomizedSearchCV
# Grid Search
param_grid = {'n_estimators': [50, 100, 200], 'max_depth': [5, 10, 15]}
grid_search = GridSearchCV(model, param_grid, cv=5)
grid_search.fit(X_train, y_train)
# Random Search
param_dist = {'n_estimators': [50, 100, 200], 'max_depth': [5, 10, 15]}
random_search = RandomizedSearchCV(model, param_dist, n_iter=10, cv=5, random_state=42)
random_search.fit(X_train, y_train)
您需要删除没有下雨的日子，然后找到中位数。
def median_rainfall(df_rain):
# Remove days with no rain
df_rain_filtered = df_rain[df_rain['rainfall'] > 0]
# Find the median amount of rainfall
median_rainfall = df_rain_filtered['rainfall'].median()
return median_rainfall
您可以使用 pandas 来计算并填充中值。
def impute_median_price(df, column):
median_price = df[column].median()
df[column].fillna(median_price, inplace=True)
return df
def fill_none(input_list):
prev_value = None
result = []
for value in input_list:
if value is None:
result.append(prev_value)
else:
result.append(value)
prev_value = value
return result
def grades_colors(df_students):
filtered_df = df_students[(df_students["grade"] > 90) & (df_students["favorite_color"].isin(["green", "red"]))]
return filtered_df
import pandas as pd
from scipy import stats
def calculate_t_value(df, column, mu_0):
sample_mean = df[column].mean()
sample_std = df[column].std()
n = len(df)
t_value = (sample_mean - mu_0) / (sample_std / (n ** 0.5))
return t_value
# Example usage
t_value = calculate_t_value(df, 'var', mu_0)
print(t_value)
import numpy as np
import pandas as pd
def euclidean_distance(point1, point2):
return np.sqrt(np.sum((point1 - point2) ** 2))
def kNN(k, data, new_point):
distances = data.apply(lambda row: euclidean_distance(row[:-1], new_point), axis=1)
sorted_indices = distances.sort_values().index
top_k = data.iloc[sorted_indices[:k]]
return top_k['label'].mode()[0]
# Example usage
data = pd.DataFrame({
'feature1': [1, 2, 3, 4],
'feature2': [2, 3, 4, 5],
'label': [0, 0, 1, 1]
})
new_point = [2.5, 3.5]
k = 3
result = kNN(k, data, new_point)
print(result)
Note: This example uses simplified assumptions to meet the interview constraints.
import pandas as pd
import numpy as np
def create_tree(dataframe, new_point):
unique_classes = dataframe['class'].unique()
for col in dataframe.columns[:-1]: # Exclude the 'class' column
if new_point[col] == 1:
sub_data = dataframe[dataframe[col] == 1]
if len(sub_data) > 0:
return sub_data['class'].mode()[0]
return unique_classes[0] # Default to the most frequent class
def random_forest(df, new_point, n_trees):
results = []
for _ in range
n_trees):
tree_result = create_tree(df, new_point)
results.append(tree_result)
# Majority vote
return max(set(results), key=results.count)
# Example usage
df = pd.DataFrame({
'feature1': [0, 1, 1, 0],
'feature2': [0, 0, 1, 1],
'class': [0, 1, 1, 0]
})
new_point = {'feature1': 1, 'feature2': 0}
n_trees = 5
result = random_forest(df, new_point, n_trees)
print(result)
import pandas as pd
import numpy as np
def sigmoid(z):
return 1 / (1 + np.exp(-z))
def logistic_regression(X, y, num_iterations, learning_rate):
weights = np.zeros(X.shape[1])
for i in range(num_iterations):
z = np.dot(X, weights)
predictions = sigmoid(z)
errors = y - predictions
gradient = np.dot(X.T, errors)
gradient = np.dot(X.T, errors)
weights += learning_rate * gradient
return weights
# Example usage
df = pd.DataFrame({
'feature1': [0, 1, 1, 0],
'feature2': [0, 0, 1, 1],
'class': [0, 1, 1, 0]
})
X = df[['feature1', 'feature2']].values
y = df['class'].values
num_iterations = 1000
learning_rate = 0.01
weights = logistic_regression(X, y, num_iterations, learning_rate)
print(weights)
import numpy as np
def k_means(data_points, k, initial_centroids):
centroids = initial_centroids
while True:
distances = np.linalg.norm(data_points[:, np.newaxis] - centroids, axis=2)
clusters = np.argmin(distances, axis=1)
new_centroids = np.array([data_points[clusters == i].mean(axis=0) for i in range(k)])
if np.all(centroids == new_centroids):
break
centroids = new_centroids
return clusters
# Example usage
data_points = np.array([[1, 2], [1, 4], [1, 0], [10, 2], [10, 4], [10, 0]])
k = 2
initial_centroids = np.array([[1, 2], [10, 2]])
clusters = k_means(data_points, k, initial_centroids)
print(clusters)
Machine Learning is a field of artificial intelligence focused on building algorithms that enable computers to learn from data without explicit programming. It uses algorithms to analyze and identify patterns in data and make predictions based on those patterns.
"Machine learning is a branch of artificial intelligence that involves creating algorithms capable of learning from and making predictions based on data. It works by training a model on a dataset and then using that model to make predictions on new data."
There are three main types of machine learning algorithms:
Supervised Learning: Useslabeled data and makes predictions based on this information. Examples include linear regression and classification algorithms.
Unsupervised Learning: Processes unlabeled data and seeks to find patterns or relationships in it. Examples include clustering algorithms like K-means.
Reinforcement Learning: The algorithm learns from interacting with its environment, receiving rewards or punishments for certain actions. Examples include training AI agents in games.
"There are three main types of machine learning algorithms: supervised learning, unsupervised learning, and reinforcement learning. Supervised learning uses labeled data to make predictions, unsupervised learning finds patterns in unlabeled data, and reinforcement learning learns from interactions with the environment to maximize rewards."
Cross-validation is a technique to evaluate the performance of a machine learning model by dividing the dataset into two parts: a training set and a validation set. The training set trains the model, whereas the validation set evaluates it.
"Cross-validation is a technique used to evaluate a machine learning model'sperformance by dividing the dataset into training and validation sets. It helps ensure the model generalizes well to new data, preventing overfitting and providing a more accurate measure of performance."
Artificial Neural Networks (ANNs) are models inspired by the human brain's structure. They consist of layers of interconnected nodes (neurons) that process input data and generate output predictions.
"An artificial neural network is a machine learning model inspired by the structure and function of the human brain. It comprises layers of interconnected neurons that process input data through weighted connections to make predictions."
Decision Trees are models for classification and regression tasks that split data into subsets based on the values of input variables to generate prediction rules.
"A decision tree is a tree-like model used for classification and regression tasks. It works by recursively splitting data into subsets based on input variables, creating rules for making predictions."
K-Nearest Neighbors (KNN) is a simple machine learning algorithm usedfor classification or regression tasks. It determines the k closest data points in the feature space to a given unseen data point and classifies it based on the majority class of its k nearest neighbors.
"The K-Nearest Neighbors (KNN) algorithm is a machine learning technique used for classification or regression. It works by identifying the k closest data points to a given point in the feature space and classifying it based on the majority class among the k nearest neighbors."
Support Vector Machines (SVM) are linear models used for binary classification and regression tasks. They find the most suitable boundary (hyperplane) that separates data into classes. Data points closest to the hyperplane, called support vectors, play a critical role in defining this boundary.
"The Support Vector Machine (SVM) algorithm is a linear model used for binary classification and regression tasks. It identifies the best hyperplane that separates data into classes, relying heavily on the data points closest to the hyperplane, known as support vectors."
Regularization is a technique to prevent overfitting in machinelearning models by adding a penalty term to the loss function. This penalty discourages the model from learning overly complex relationships in the data.
"Regularization is a technique to prevent overfitting in machine learning models by adding a penalty term to the loss function, which discourages the model from learning overly complex patterns. Common types of regularization include L1 (Lasso) and L2 (Ridge) regularization."
from sklearn.linear_model import Ridge # Applying L2 Regularization (Ridge Regression) ridge_model = Ridge(alpha=1.0) ridge_model.fit(X_train, y_train)
Gradient Descent is an optimization algorithm used to minimize a cost function in machine learning. It iteratively adjusts the parameters of the model in the direction of the negative gradient of the cost function until it reaches a minimum.
"Gradient Descent is an optimization algorithm used to minimize a cost function in machine learning. It iteratively updates the model parameters in the direction of the negative gradient of the cost function, aiming to find the parameters that minimize the cost."
Ensemble Learning is a technique where multiple models (often called "weak learners") are combined to solve a prediction task. The combined model is generally more robust and performs better than individual models.
"Ensemble learning is a machine learning technique where multiple models are combined to solve a prediction task. Common ensemble methods include bagging, boosting, and stacking. Combining the predictions of individual models can improve performance and reduce the risk of overfitting."
from sklearn.ensemble import RandomForestClassifier # Ensemble learning using Random Forest model = RandomForestClassifier(n_estimators=100, max_depth=10, random_state=42) model.fit(X_train, y_train) predictions = model.predict(X_test)
Preparing for a Python machine learning interview involves understanding both theoretical concepts and practical implementations. This guide has covered several essential questions and answers that frequently come up in interviews. By familiarizing yourself with these topics and practicing the provided code examples, you'll be well-equipped to handle a wide range of questions in your next machine learning interview. Good luck!
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