From 53d017da45545df5d3205bbe7bca151ec42902a0 Mon Sep 17 00:00:00 2001
From: aikataumyan <251zs01311@student.zen.ac.jp>
Date: Tue, 10 Feb 2026 05:26:54 +0900
Subject: [PATCH] =?UTF-8?q?=E3=83=A9=E3=83=B3=E3=82=AD=E3=83=B3=E3=82=B0?=
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---
 app.js | 42 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 42 insertions(+)

diff --git a/app.js b/app.js
index ad9a93a..3d4a260 100644
--- a/app.js
+++ b/app.js
@@ -1 +1,43 @@
 'use strict';
+const fs = require('node:fs');
+const readline = require('node:readline');
+const rs = fs.createReadStream('./popu-pref.csv');
+const rl = readline.createInterface({ input: rs });
+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 === 2016 || year === 2021) {
+let value = null;
+    if (prefectureDataMap.has(prefecture)) {
+      value = prefectureDataMap.get(prefecture);
+    } else {
+      value = {
+        before: 0,
+        after: 0,
+        change: null
+      };
+    }
+    if (year === 2016) {
+      value.before = popu;
+    }
+    if (year === 2021) {
+      value.after = popu;
+    }
+    prefectureDataMap.set(prefecture, value);
+  }
+});
+rl.on('close', () => {
+    for (const [key, value] of prefectureDataMap) {
+    value.change = value.after / value.before;
+  }
+    const rankingArray = Array.from(prefectureDataMap).sort((pair1, pair2) => {
+    return pair2[1].change - pair1[1].change;
+  });
+  const rankingStrings = rankingArray.map(([key, value]) => {
+    return `${key}: ${value.before}=>${value.after} 変化率: ${value.change}`;
+  });
+  console.log(rankingStrings);
+});
\ No newline at end of file