{"id":25683,"date":"2024-03-16T05:24:59","date_gmt":"2024-03-16T05:24:59","guid":{"rendered":"https:\/\/www.silicloud.com\/blog\/how-to-write-knn-algorithm-python-code\/"},"modified":"2024-03-22T06:45:57","modified_gmt":"2024-03-22T06:45:57","slug":"how-to-write-knn-algorithm-python-code","status":"publish","type":"post","link":"https:\/\/www.silicloud.com\/blog\/how-to-write-knn-algorithm-python-code\/","title":{"rendered":"How to write KNN algorithm Python code?"},"content":{"rendered":"<p>Here is a simple Python code example for the KNN algorithm.<\/p>\n<pre class=\"post-pre\"><code><span class=\"hljs-keyword\">import<\/span> numpy <span class=\"hljs-keyword\">as<\/span> np\r\n<span class=\"hljs-keyword\">from<\/span> collections <span class=\"hljs-keyword\">import<\/span> Counter\r\n\r\n<span class=\"hljs-keyword\">def<\/span> <span class=\"hljs-title function_\">euclidean_distance<\/span>(<span class=\"hljs-params\">x1, x2<\/span>):\r\n    <span class=\"hljs-keyword\">return<\/span> np.sqrt(np.<span class=\"hljs-built_in\">sum<\/span>((x1 - x2) ** <span class=\"hljs-number\">2<\/span>))\r\n\r\n<span class=\"hljs-keyword\">class<\/span> <span class=\"hljs-title class_\">KNN<\/span>:\r\n    <span class=\"hljs-keyword\">def<\/span> <span class=\"hljs-title function_\">__init__<\/span>(<span class=\"hljs-params\">self, k=<span class=\"hljs-number\">3<\/span><\/span>):\r\n        self.k = k\r\n    \r\n    <span class=\"hljs-keyword\">def<\/span> <span class=\"hljs-title function_\">fit<\/span>(<span class=\"hljs-params\">self, X, y<\/span>):\r\n        self.X_train = X\r\n        self.y_train = y\r\n    \r\n    <span class=\"hljs-keyword\">def<\/span> <span class=\"hljs-title function_\">predict<\/span>(<span class=\"hljs-params\">self, X<\/span>):\r\n        y_pred = [self._predict(x) <span class=\"hljs-keyword\">for<\/span> x <span class=\"hljs-keyword\">in<\/span> X]\r\n        <span class=\"hljs-keyword\">return<\/span> np.array(y_pred)\r\n    \r\n    <span class=\"hljs-keyword\">def<\/span> <span class=\"hljs-title function_\">_predict<\/span>(<span class=\"hljs-params\">self, x<\/span>):\r\n        <span class=\"hljs-comment\"># \u8ba1\u7b97\u6240\u6709\u8bad\u7ec3\u6837\u672c\u4e0e\u5f85\u9884\u6d4b\u6837\u672c\u7684\u8ddd\u79bb<\/span>\r\n        distances = [euclidean_distance(x, x_train) <span class=\"hljs-keyword\">for<\/span> x_train <span class=\"hljs-keyword\">in<\/span> self.X_train]\r\n        <span class=\"hljs-comment\"># \u6839\u636e\u8ddd\u79bb\u6392\u5e8f\u5e76\u83b7\u53d6\u524dk\u4e2a\u6837\u672c\u7684\u7d22\u5f15<\/span>\r\n        k_indices = np.argsort(distances)[:self.k]\r\n        <span class=\"hljs-comment\"># \u83b7\u53d6\u524dk\u4e2a\u6837\u672c\u7684\u6807\u7b7e<\/span>\r\n        k_labels = [self.y_train[i] <span class=\"hljs-keyword\">for<\/span> i <span class=\"hljs-keyword\">in<\/span> k_indices]\r\n        <span class=\"hljs-comment\"># \u8fd4\u56de\u51fa\u73b0\u6b21\u6570\u6700\u591a\u7684\u6807\u7b7e\u4f5c\u4e3a\u9884\u6d4b\u7ed3\u679c<\/span>\r\n        most_common = Counter(k_labels).most_common(<span class=\"hljs-number\">1<\/span>)\r\n        <span class=\"hljs-keyword\">return<\/span> most_common[<span class=\"hljs-number\">0<\/span>][<span class=\"hljs-number\">0<\/span>]\r\n<\/code><\/pre>\n<p>Example of use:<\/p>\n<pre class=\"post-pre\"><code>X_train = np.array([[<span class=\"hljs-number\">1<\/span>, <span class=\"hljs-number\">2<\/span>], [<span class=\"hljs-number\">1.5<\/span>, <span class=\"hljs-number\">1.8<\/span>], [<span class=\"hljs-number\">5<\/span>, <span class=\"hljs-number\">8<\/span>], [<span class=\"hljs-number\">8<\/span>, <span class=\"hljs-number\">8<\/span>], [<span class=\"hljs-number\">1<\/span>, <span class=\"hljs-number\">0.6<\/span>], [<span class=\"hljs-number\">9<\/span>, <span class=\"hljs-number\">11<\/span>]])\r\ny_train = np.array([<span class=\"hljs-number\">0<\/span>, <span class=\"hljs-number\">0<\/span>, <span class=\"hljs-number\">1<\/span>, <span class=\"hljs-number\">1<\/span>, <span class=\"hljs-number\">0<\/span>, <span class=\"hljs-number\">1<\/span>])\r\n\r\nknn = KNN(k=<span class=\"hljs-number\">3<\/span>)\r\nknn.fit(X_train, y_train)\r\n\r\nX_test = np.array([[<span class=\"hljs-number\">2<\/span>, <span class=\"hljs-number\">3<\/span>], [<span class=\"hljs-number\">6<\/span>, <span class=\"hljs-number\">9<\/span>], [<span class=\"hljs-number\">1<\/span>, <span class=\"hljs-number\">1<\/span>]])\r\ny_pred = knn.predict(X_test)\r\n\r\n<span class=\"hljs-built_in\">print<\/span>(y_pred)  <span class=\"hljs-comment\"># \u8f93\u51fa\uff1a[0, 1, 0]<\/span>\r\n<\/code><\/pre>\n<p>In this example, the Euclidean distance is used as the distance metric method, and a simple KNN class is implemented, where the fit() method is used to train the model, the predict() method is used to predict the labels of new samples. The _predict() method of the KNN class is used to calculate the prediction result for a single sample.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Here is a simple Python code example for the KNN algorithm. import numpy as np from collections import Counter def euclidean_distance(x1, x2): return np.sqrt(np.sum((x1 &#8211; x2) ** 2)) class KNN: def __init__(self, k=3): self.k = k def fit(self, X, y): self.X_train = X self.y_train = y def predict(self, X): y_pred = [self._predict(x) for x in [&hellip;]<\/p>\n","protected":false},"author":10,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_import_markdown_pro_load_document_selector":0,"_import_markdown_pro_submit_text_textarea":"","footnotes":""},"categories":[1],"tags":[],"class_list":["post-25683","post","type-post","status-publish","format-standard","hentry","category-uncategorized"],"yoast_head":"<!-- This site is optimized with the Yoast SEO Premium plugin v21.5 (Yoast SEO v21.5) - https:\/\/yoast.com\/wordpress\/plugins\/seo\/ -->\n<title>How to write KNN algorithm Python code? 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