Master 2020 を練習問題の通りに変更

app.js

@@ -1 +1,42 @@
 '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) { //　都道府県のデータがなかった場合
+      // データの初期化
+      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 rankingStrings = rankingArray.map(([key, value], i) => {
+        return (i + 1) + "位" + key + ': ' + value.popu10 + '=>' + value.popu15 + ' 変化率:' + value.change;
+    })
+      console.log(rankingStrings);
+});