From 6a659cb8020de47d8087029a02c0d319f99d1c60 Mon Sep 17 00:00:00 2001
From: yako123987 <iyoudou054224@gmail.com>
Date: Sun, 3 May 2026 15:05:14 +0900
Subject: [PATCH] =?UTF-8?q?=E3=83=A9=E3=83=B3=E3=82=AD=E3=83=B3=E3=82=B0?=
 =?UTF-8?q?=E3=81=AE=E5=AE=9F=E8=A3=85=E5=AE=8C=E4=BA=86?=
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---
 app.js | 44 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 44 insertions(+)

diff --git a/app.js b/app.js
index ad9a93a..8a8c7d7 100644
--- a/app.js
+++ b/app.js
@@ -1 +1,45 @@
 'use strict';
+const fs=require('node:fs');
+const readline=require('node:readline');
+const re =fs.createReadStream('./popu-pref.csv');
+const rl =readline.createInterface({input:re});
+const prefectureDataMap=new Map();
+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);
+} )
+
+