如何在lodash forEach中创建一个回调函数来填充数组? [英] How can I make a callback function in the lodash forEach populate an array?

问题描述

我有以下代码:

$scope.option.cityMap = data.reduce(function (rv, v) {
                       rv[v.cityId] = v;
                       return rv;
                   }, {});

有人可以告诉我如何使用_.lodash forEach实现此功能吗?我看了看文档，但是我不确定如何实现回调函数，所以它会创建一个数组.

Can someone tell me how I can implement this with the _.lodash forEach ? I have looked at the docs but I am not sure how to implement the callback function so it creates an array.

$scope.option.cityMap = _.forEach(data, 

推荐答案

使用功能助手，所有解决方案的效率都低于命令式":

Using the functional helpers all solutions are less efficient than "imperative style":

var cityMap = {};
var len = data.length;
for (var i = 0; i < len; i++) {
  cityMap[data[i].cityId] = data[i];
}
// return cityMap;

如果性能确实是一个问题，请从上方进行操作.如果从外部看(数据输入，数据输出，无副作用)，它是纯净的且实用的.

If performance is really an issue, make a function from above. It's pure and functional, if looked from outside (data in, data out, no side-effects).

您还可以使用 _.zipObject :

You can also use _.zipObject:

var cityMap = _(data).map(data, function (v) {
  return [v.cityId, v];
}).zipObject().value();

或 reduce ，因为我们没有复制累加器rv(从某种意义上讲是作弊)，它也应该非常有效.

or reduce, as we are not copying the accumulator rv (cheating in a sense), it should be quite efficient as well.

var cityMap = _.reduce(data, function (rv, v) {
  rv[v.cityId] = v;
  return rv;
}, {});

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