2010 年から 2015 年にかけて 15〜19 歳の人が減った割合の都道府県ランキング

app.js

@@ -1 +1,51 @@
 'use strict';
+const fs = require('fs');
+const readline =require('readline');
+const rs =fs.createReadStream('./popu-pref.csv');
+const rl =readline.createInterface({input: rs, output: {} });
+const prefectureDataMap =new Map();
+// key: 都道府県 value: 集計データのオブジェクト
+
+
+
+rl.on('line', lineString =>{
+    const columns =lineString.split(',');
+    const year =parseInt(columns[0]);
+    const prefecture =columns[1];
+    const popu =parseInt(columns[3]);
+
+    if(year===2010 ||year===2015){
+
+        let value =prefectureDataMap.get(prefecture);
+        if(!value){
+            value ={
+                popu10: 0,
+                popu15: 0,
+                change: null
+            };
+        }
+        if(year===2010){
+            value.popu10 =popu;
+        }
+        if(year===2015){
+            value.popu15 =popu;
+        }
+        prefectureDataMap.set(prefecture, value);
+    }
+});
+rl.on('close', () => {
+    for(let [key, value] of prefectureDataMap){
+        value.change =value.popu15 / value.popu10;
+    }
+
+    const rankingArray =Array.from(prefectureDataMap).sort((pair1, pair2) => {
+        return pair1[1].change - pair2[1].change;
+    });
+    const rankingString =rankingArray.map(([key, value],i) =>{
+        return ((i+1) + '位: '+key + ': ' + value.popu10 + '=>' + value.popu15 + ' 変化率: ' + value.change);
+    });
+
+    console.log(rankingString);
+});
+
+