下划线或lazy.js映射（0,1,2,3,4）+（1,2,3,4,5）->（1,3,5,7,9）

Question

I want to map a sequence to another sequence such as

map (0,1,2,3,4) + (1,2,3,4,5) -> (1,3,5,7,9)

How to do that in lazy.js or underscore ?

Thanks!

Answer 1

You can use _.zip and _.map , like this

var _ = require("underscore");

function sum(numbers) {
    var result = 0;
    for (var i = 0; i < numbers.length; i += 1) {
        result += numbers[i];
    }
    return result;
}

console.log(_.map(_.zip([0, 1, 2, 3, 4], [1, 2, 3, 4, 5]), sum))
// [ 1, 3, 5, 7, 9 ]

Since only two numbers are going to be there, always, you can simplify that like this

var result = _.chain([0, 1, 2, 3, 4])
    .zip([1, 2, 3, 4, 5])
    .map(function(numbers) {
        return numbers[0] + numbers[1];
    })
    .value();

console.log(result);

You can make it a little more generic and clean, like this

function sum(numbers) {
    return numbers.reduce(function(result, current) {
        return result + current;
    }, 0);
}

var result = _.chain([0, 1, 2, 3, 4])
    .zip([1, 2, 3, 4, 5])
    .map(sum)
    .value();

Or even simpler, like in the first answer

console.log(_.map(_.zip([0, 1, 2, 3, 4], [1, 2, 3, 4, 5]), sum));

Answer 2

The above example can be achieved in the following way using underscore:

_.map([0, 1, 2, 3, 4], function(n, i) {
  return n + i + 1
}) // This returns [1, 3, 5, 7, 9]

Here's a link to the API docs: Underscore#map

Answer 3

Using underscore, @thefortheye's solution works well, here's a similar solution just using lazy.js instead;

> var Lazy = require('lazy.js');

> var addParts = function(x) { return Lazy(x).sum(); }

> Lazy([0,1,2,3,4]).zip([1,2,3,4,5]).map(addParts).toArray()

[ 1, 3, 5, 7, 9 ]