[Ramda] R.project -- Select a Subset of Properties from a Collection of Objects in Ramda

In this lesson we‘ll take an array of objects and map it to a new array where each object is a subset of the original. We‘ll look at multiple ways to accomplish this, refactoring our code into a simple and easy to read function using Ramda‘s map, pick and project functions.

Lets say we have an array of objects, we want to only pick the ‘name‘ and ‘price‘ props from each object:

const products = [
  {name: ‘Jeans‘, price:80, category: ‘clothes‘},
  {name: ‘Hoodie‘, price:60, category: ‘clothes‘},
  {name: ‘Jacket‘, price:120, category: ‘clothes‘},
  {name: ‘Cards‘, price: 35, category: ‘games‘},
  {name: ‘iPhone‘, price: 649, category: ‘electronics‘},
  {name: ‘Sauce Pan‘, price: 100, category: ‘housewares‘}
  ]

const result = products.map(p => ({name: p.name, price: p.price}))

console.log(result);

It works but as we can image that if we need to pick 10 props or even more, then it would be a problem, the code would be hard to read.

We can improve this by using Ramda‘s pick method:

const result = products.map(p => R.pick([‘name‘, ‘price‘], p))

Then we can utilize Ramda automaticlly curry function to improve the code:

const result = products.map(R.pick([‘name‘, ‘price‘]))

Then we can extract the bussniess logic into a sprate function to make it resuable:

const getNameAndPrice = R.map(R.pick([‘name‘, ‘price‘]));
const result = getNameAndPrice(products);

Since it is a common pattern that "map to each object in array and pick certain props will it",  we can use "R.project":

const getNameAndPrice = R.project([‘name‘, ‘price‘]);
const result = getNameAndPrice(products);

[Ramda] R.project -- Select a Subset of Properties from a Collection of Objects in Ramda

原文：http://www.cnblogs.com/Answer1215/p/6297152.html