練習問題の解答

app.js

@@ -1,42 +1,64 @@
 'use strict';
+
 const fs = require('fs');
 const readline = require('readline');
 const rs = fs.ReadStream('./popu-pref.csv');
-const rl = readline.createInterface({ 'input': rs, 'output': {} });
+const rl = readline.createInterface({'input':rs, 'output':{}});
+const map = new Map(); //key: 都道府県, value: 集計データのオブジェクト
 
-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', (line) => {
-    const columns = line.split(',');
-    const year = columns[0];
+rl.on('line', (lineString) => 
+{
+    const columns = lineString.split(',');
+    const year = parseInt(columns[0]);
     const prefecture = columns[2];
-    const popu = columns[7];
-    if (year === '2010' || year === '2015') {
-        let value = prefectureDataMap.get(prefecture);
-        if (!value) {
-            value = {
-                popu10: 0,
-                popu15: 0,
+    const popu = parseInt(columns[7]);
+
+    if (year === 2010 || year === 2015) 
+    {
+        let value = map.get(prefecture);
+        if (!value)
+        {
+            value = 
+            {
+                popu10: 0, 
+                popu15: 0, 
                 change: null
             };
-        }
-        if (year === '2010') {
-            value.popu10 += parseInt(popu);
-        }
-        if (year === '2015') {
-            value.popu15 += parseInt(popu);
-        }
-        prefectureDataMap.set(prefecture, value);
+        }  
+        if (year === 2010) value.popu10 += popu;
+        if (year === 2015) value.popu15 += popu;
+
+        map.set(prefecture, value);
     }
 });
-rl.on('close', () => {
-    for (let [key, value] of prefectureDataMap) {
-        value.change = value.popu15 / value.popu10;
+
+rl.resume();
+rl.on('close', () => 
+{
+    for (const pair of map) 
+    {
+        const value = pair[1];
+        value.change = value.popu15 / value.popu10;        
     }
-    const rankingArray = Array.from(prefectureDataMap).sort((pair1, pair2) => {
-        return pair2[1].change - pair1[1].change;
+
+    //降順に並び替え
+    /*
+    pair2[1] - pair1[1] > 0ならpair2 -> pair1に
+    pair2[1] - pair1[1] < 0ならpair1 -> pair2に
+    pair2[1] - pair1[1] = 0ならそのまま
+
+    Array.from(map)で配列として呼び出し(pair[0] = 都道府県, pair[1] = value)
+    */
+    const rankingArray = Array.from(map).sort((pair1, pair2) => 
+    {
+        return (pair2[1].change - pair1[1].change) * (-1);
     });
-    const rankingStrings = rankingArray.map(([key, value]) => {
-        return key + ': ' + value.popu10 + '=>' + value.popu15 + ' 変化率:' + value.change;
+
+    const rankingStrings = rankingArray.map((pair, i) => 
+    {
+        return (i+1) + '位 ' + pair[0] + ': ' + pair[1].popu10 + '=>' + pair[1].popu15 + '変化率: ' + pair[1].change;
     });
+
     console.log(rankingStrings);
 });
+