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<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>2</title>
<script>const {log, clear} = console;</script>
<script src="fx.js"></script>
</head>
<body>
6. 축약하는 함수 reduce
- reduce, add
<script type="module">
log(reduce(add, 0, [1, 2, 3]));
log(reduce(add, [1, 2, 3]));
log(reduce(add, 1, [2, 3]));
log(add(add(add(0, 1), 2), 3));
</script>
- count
<script type="module">
const inc = (obj, k) => {
obj[k] = (obj[k] || 0) + 1;
return obj;
};
const count = iterable => reduce(inc, {}, iterable);
log(count([1, 2, 3, 1, 1, 2, 3, 3, 3, 4]));
</script>
7. 함수를 다루는 함수
- go
- pipe
<script type="module">
// const go = (a, f1, f2, f3) => f3(f2(f1(a)));
const go = (a, ...fs) => reduce((a, f) => f(a), a, fs);
go(
0,
a => a + 1,
a => a + 10,
a => a + 100,
log);
const pipe = (...fs) => (a) => go(a, ...fs);
const f = pipe(
a => a + 1,
a => a + 10,
a => a + 100);
log(f(0))
</script>
- curry
<script type="module">
const curry = f => (a, ..._) =>
_.length ?
f(a, ..._) :
(..._) => f(a, ..._);
const add = curry((a, b) => a + b);
log(add(10)(5));
log(add(10, 5));
clear();
log(
reduce(add, 0,
L.take(3,
L.map(a => a * a,
L.filter(a => a % 2, [1, 2, 3, 4, 5, 6, 7])))));
go([1, 2, 3, 4, 5, 6, 7],
L.map(a => a * a),
L.filter(a => a % 2),
L.take(3),
reduce(add),
log);
</script>
8. 2차원 배열 다루기 flat
- L.flat
<script type="module">
const isIterable = iter =>
Boolean(iter && iter[Symbol.iterator]);
// L.flat = function* (iterable) {
// for (const a of iterable) {
// if (isIterable(a)) {
// yield* a;
// } else {
// yield a;
// }
// }
// };
// log([...L.flat([[1, 2, 3], [4, 5], [6, 7]])]);
go(
[[1, 2, 3], [4, 5], [6, 7]],
L.flat,
L.map(a => a * a),
L.filter(a => a % 2),
reduce(add),
log);
</script>
- 리얼월드, users
<script type="module">
const users = [
{ name: 'a', age: 21, family: [
{ name: 'a1', age: 53 }, { name: 'a2', age: 47 },
{ name: 'a3', age: 16 }, { name: 'a4', age: 14 }
] },
{ name: 'b', age: 24, family: [
{ name: 'b1', age: 58 }, { name: 'b2', age: 51 },
{ name: 'b3', age: 10 }, { name: 'b4', age: 22 }
] },
{ name: 'c', age: 31, family: [
{ name: 'c1', age: 64 }, { name: 'c2', age: 62 }
] },
{ name: 'd', age: 20, family: [
{ name: 'd1', age: 42 }, { name: 'd2', age: 42 },
{ name: 'd3', age: 11 }, { name: 'd4', age: 7 }
] }
];
go(
users,
L.map(u => u.family),
L.flat,
L.map(u => u.age),
L.filter(age => age < 20),
L.take(2),
reduce(add),
log);
clear();
const flatMap = curry(pipe(L.map, L.flat));
log(...flatMap(a => L.range(0, a), [1, 2]));
</script>
9. 커머스 데이터 다루기
- 간단한 장바구니
<script type="module">
const products = [
{ name: '반팔티', price: 15000, quantity: 1, is_selected: true },
{ name: '긴팔티', price: 20000, quantity: 2, is_selected: false },
{ name: '핸드폰케이스', price: 15000, quantity: 3, is_selected: true },
{ name: '후드티', price: 30000, quantity: 4, is_selected: false },
{ name: '바지', price: 25000, quantity: 5, is_selected: false }
];
const sum = reduce(add);
const sumMap = curry(pipe(L.map, sum));
const totalQuantity = sumMap(p => p.quantity);
const totalQuantitySelected = pipe(
L.filter(p => p.is_selected),
totalQuantity);
const totalPrice = sumMap(p => p.price);
const totalPriceSelected = pipe(
L.filter(p => p.is_selected),
totalPrice);
log(totalQuantity(products));
log(totalQuantitySelected(products));
log(totalPrice(products));
log(totalPriceSelected(products));
</script>
- 복잡한 장바구니
<script type="module">
const products = [
{
name: '반팔티', price: 15000, is_selected: true,
options: [
{ name: 'M', price: 0, quantity: 1 },
{ name: 'L', price: 0, quantity: 2 },
{ name: 'XL', price: 2000, quantity: 3 }
]
},
{
name: '긴팔티', price: 20000, is_selected: false,
options: [
{ name: 'M', price: 0, quantity: 1 },
{ name: 'L', price: 0, quantity: 2 },
{ name: 'XL', price: 2000, quantity: 3 }
]
},
{
name: '핸드폰케이스', price: 15000, is_selected: true,
options: [
{ name: '유광', price: 0, quantity: 1 },
{ name: '무광', price: 0, quantity: 2 },
{ name: '범퍼케이스', price: 4000, quantity: 3 }
]
}
];
go(
products,
L.filter(p => p.is_selected),
L.map(p => p.options),
L.flat,
L.map(o => o.quantity),
reduce(add),
log);
go(
products,
// L.filter(p => p.is_selected),
L.map(p => L.map(o => (p.price + o.price) * o.quantity, p.options)),
L.flat,
reduce(add),
log);
</script>
</body>
</html>