Optimize examples, add filter

tshemsedinov · tshemsedinov · commit 1840abbf77e5 · 2018-11-14T10:58:43.000+02:00
diff --git a/JavaScript/2-extended.js b/JavaScript/2-extended.js
@@ -6,7 +6,7 @@ const partial = (fn, ...args) => (...rest) => fn(...args.concat(rest));
 
 const projection = (meta, obj) => Object.keys(meta)
   .reduce((hash, key) => (hash[key] = meta[key]
-    .reduce((val, fn, i) => i ? fn(val) : obj[fn], null), hash), {});
+    .reduce((val, fn, i) => (i ? fn(val) : obj[fn]), null), hash), {});
 
 // Dataset
 
diff --git a/JavaScript/3-cached.js b/JavaScript/3-cached.js
@@ -6,7 +6,7 @@ const projection = meta => {
   const keys = Object.keys(meta);
   return obj => keys.reduce((hash, key) => (
     hash[key] = meta[key]
-      .reduce((val, fn, i) => (i === 0 ? obj[fn] : fn(val)), null),
+      .reduce((val, fn, i) => (i ? fn(val) : obj[fn]), null),
     hash), {});
 };
 
diff --git a/JavaScript/c-filter.js b/JavaScript/c-filter.js
@@ -0,0 +1,63 @@
+'use strict';
+
+// Projection
+
+const id = x => x;
+
+const projection = meta => src => meta.reduce(
+  (dest, [name, fn = id, field = name]) =>
+    (dest[name] = fn(src[field]), dest), {}
+);
+
+// Display
+
+const max = items => Math.max(...items);
+const maxProp = key => items => max(items.map(x => x[key]));
+const maxLength = maxProp('length');
+const col = (name, data) => data.map(obj => obj[name].toString());
+
+const render = meta => src => {
+  const keys = meta.map(([name]) => name);
+  const maxWidth = keys.map(key => maxLength(col(key, src)));
+  const dest = src.map(obj => maxWidth.map(
+    (width, i) => obj[keys[i]].toString().padEnd(width + 4)
+  ));
+  return dest.map(row => row.join('')).join('\n');
+};
+
+// Dataset
+
+const persons = [
+  { name: 'Marcus Aurelius', city: 'Rome', born: 121 },
+  { name: 'Victor Glushkov', city: 'Rostov on Don', born: 1923 },
+  { name: 'Ibn Arabi', city: 'Murcia', born: 1165 },
+  { name: 'Mao Zedong', city: 'Shaoshan', born: 1893 },
+  { name: 'Rene Descartes', city: 'La Haye en Touraine', born: 1596 },
+];
+
+// Metadata
+
+const year = date => date.getFullYear();
+const diff = y => year(new Date()) - year(new Date(y + ''));
+const upper = s => s.toUpperCase();
+
+const md = [
+  ['name'],
+  ['place', upper, 'city'],
+  ['age', diff, 'born'],
+];
+
+const query = person => (
+  person.name !== '' &&
+  person.born < 1900 &&
+  person.city === 'Rome'
+);
+
+// Usage
+
+const pf = projection(md);
+const data = persons.filter(query).map(pf);
+
+const renderer = render(md);
+const res = renderer(data);
+console.log('\n' + res + '\n');
diff --git a/README.md b/README.md
@@ -1,2 +1 @@
-# Projection
-Data structures projection
+# Data structures projection

Original file line number	Diff line number	Diff line change
`@@ -1,2 +1 @@`
`1`		`-# Projection`
`2`		`-Data structures projection`
	`1`	`+# Data structures projection`