2024/3/18
コードの再構成
10章無関係の下位問題を抽出する

10.1 入門的な例: findClosestLocation()

こちらの記事の続編になります。

10.1 入門的な例: findClosestLocation()

const findClosestLocation = (lat, lng array) => {
     let closest;
     let closes_dist = Number.MAX_VALUE;

     for(var i = 0; i < arrya.length; i += i){
         //2つの地点をラジアンに変換する
         const lat_rad = radians(lat);
         const lat_rad = radians(lnt);
         const lat2_rad = radians(array[i].latitude);
         const lat2_rad = radians(array[i].longitude);
    
         //「球面三角法の第二余弦定理」の公式を使う
         const dist = Math.acos(Math.sin(lat_rad) * Math.sin(lat2_rad) +
                              Math.cos(lat_rad) * Math.cos(lat2_rad) *
                              Math.cos(lang2_rad - lng_rad));
    
         if(dist < closest_dist){
            closest = array[i];
            closest_dist = dist;
         }
     }
     
     return closest;
}

javascript:ループ内の無関係の下位問題を抽出

const sphericalDistance = (lat1, lng1, lat2, lng2) => {
     const lat1_rad = radians(lat1);
     const lng1_rad = radians(lng1);
     const lat2_rad = adians(lng2);
     const lng2_rad = radians(lng2);

     return Math.acos(Math.sin(lat1_rad) * Math.sin(lat2_rad) +
                               Math.cos(lat1_rad) * Math.cos(lat2_rad) *
                               Math.cos(lng2_rad - lng_rad));
} 

const findClosestLocation = (lat, lng array) => {
     let closest;
     let closes_dist = Number.MAX_VALUE;

     for(var i = 0; i < arrya.length; i += i){
         //関数に切り出した
-        const lat_rad = radians(lat);
-        const lnt_rad = radians(lng);
-        const lat2_rad = radians(array[i].latitude);
-        const lng2_rad = radians(array[i].longitude);
    
         //「球面三角法の第二余弦定理」の公式を使う
-        const dist = Math.acos(Math.sin(lat_rad) * Math.sin(lat2_rad) +
-                             Math.cos(lat_rad) * Math.cos(lat2_rad) *
-                             Math.cos(lng2_rad - lng_rad));
         //切り出した関数を使用
+        const dist =  sphericalDistance(lat, lng, array[i].latitude, array[i].longitude) 
         if(dist < closest_dist){
            closest = array[i];
            closest_dist = dist;
         }
     }
     
     return closest;
}