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コード

app.js

@@ -1 +1,52 @@
 '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();
+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 rankingStrings = rankingArray.map(([key, value],i) => {
+        return (
+          (i + 1) + '位' +
+          key +
+          ': ' +
+          value.popu10 +
+          '=>' +
+          value.popu15 +
+          ' 変化率:' +
+          value.change
+    );
+
+      });
+    console.log(rankingStrings);
+});