blocks|key|231171|text|_.map返回一个数组，而不是一个对象。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|231172|如果你想要一个对象，你最好使用不同的函数，比如each；如果你真的想使用地图，你可以这样做：|style|CODE|231173|Object.keys(object).map(function(value,+index)+{
+++object[value]+*=+3;
})|code-block|syntax|javascript|231174|但这是令人困惑的，当看到map时，人们会期望有一个数组作为结果，然后用它做一些东西。|231175|entityMap|0|LINK|mutability|MUTABLE|url|http://underscorejs.org/#map^0|0|5|0|0|N|4|0|0|C|3|0^^$0|@$1|2|3|4|5|6|7|W|8|@]|9|@$A|X|B|Y|1|Z]]|C|$]]|$1|D|3|E|5|6|7|10|8|@$A|11|B|12|F|G]]|9|@]|C|$]]|$1|H|3|I|5|J|7|13|8|@]|9|@]|C|$K|L]]|$1|M|3|N|5|6|7|14|8|@$A|15|B|16|F|G]]|9|@]|C|$]]|$1|O|3|-4|5|6|7|17|8|@]|9|@]|C|$]]]|P|$Q|$5|R|S|T|C|$U|V]]]]

<p><a href="http://underscorejs.org/#map" rel="nofollow">_.map</a> returns an Array, not an Object.</p>

<p>If you want an object you're better off using a different function, like <code>each</code>; if you really want to use map you could do something like this:</p>

<pre><code>Object.keys(object).map(function(value, index) {
   object[value] *= 3;
})
</code></pre>

<p>but that is confusing, when seeing <code>map</code> one would expect to have an array as result and then make something with it.</p>


blocks|key|231210|text|我认为您需要一个mapValues函数(将一个函数映射到对象的值上)，它很容易实现：|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|231211|mapValues+=+function(obj,+f)+{
++var+k,+result,+v;
++result+=+{};
++for+(k+in+obj)+{
++++v+=+obj[k];
++++result[k]+=+f(v);
++}
++return+result;
};|code-block|syntax|javascript|231212|entityMap|0|LINK|mutability|MUTABLE|url|http://lodash.com/docs#mapValues^0|8|9|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@$A|R|B|S|1|T]]|C|$]]|$1|D|3|E|5|F|7|U|8|@]|9|@]|C|$G|H]]|$1|I|3|-4|5|6|7|V|8|@]|9|@]|C|$]]]|J|$K|$5|L|M|N|C|$O|P]]]]

<p>I think you want a <a href="http://lodash.com/docs#mapValues" rel="nofollow">mapValues</a> function (to map a function over the values of an object), which is easy enough to implement yourself:</p>

<pre><code>mapValues = function(obj, f) {
  var k, result, v;
  result = {};
  for (k in obj) {
    v = obj[k];
    result[k] = f(v);
  }
  return result;
};
</code></pre>


blocks|key|14893|text|​|type|unstyled|depth|inlineStyleRanges|entityRanges|data|14894|var+mapped+=+_.reduce({+one:+1,+two:+2,+three:+3+},+function(obj,+val,+key)+{
++++obj[key]+=+val*3;
++++return+obj;
},+{});

console.log(mapped);|code-block|syntax|javascript|14895|<script+src="http://underscorejs.org/underscore-min.js"></script>
<script+src="https://getfirebug.com/firebug-lite-debug.js"></script>|14896|14897|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|M|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|I|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|J|3|-4|5|6|7|P|8|@]|9|@]|A|$]]]|K|$]]

<p><div class="snippet" data-lang="js" data-hide="false">
<div class="snippet-code">
<pre class="snippet-code-js lang-js prettyprint-override"><code>var mapped = _.reduce({ one: 1, two: 2, three: 3 }, function(obj, val, key) {
    obj[key] = val*3;
    return obj;
}, {});

console.log(mapped);</code></pre>
<pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;script src="http://underscorejs.org/underscore-min.js"&gt;&lt;/script&gt;
&lt;script src="https://getfirebug.com/firebug-lite-debug.js"&gt;&lt;/script&gt;</code></pre>
</div>
</div>
</p>


blocks|key|231227|text|我知道这是旧的，但现在下划线有了一个新的对象地图：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|231228|_.mapObject(object,+iteratee,+[context])+|code-block|syntax|javascript|231229|当然，您可以为数组和对象构建灵活的映射|231230|_.fmap+=+function(arrayOrObject,+fn,+context){
++++if(this.isArray(arrayOrObject))
++++++return+_.map(arrayOrObject,+fn,+context);
++++else
++++++return+_.mapObject(arrayOrObject,+fn,+context);
}|231231|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

<p>I know this is old, but now Underscore has a new map for objects :</p>

<pre><code>_.mapObject(object, iteratee, [context]) 
</code></pre>

<p>You can of course build a flexible map for both arrays and objects</p>

<pre><code>_.fmap = function(arrayOrObject, fn, context){
    if(this.isArray(arrayOrObject))
      return _.map(arrayOrObject, fn, context);
    else
      return _.mapObject(arrayOrObject, fn, context);
}
</code></pre>


blocks|key|231237|text|您可以在Lodash中使用_.mapValues(users,+function(o)+{+return+o.age;+});，在下划线中使用_.mapObject({+one:+1,+two:+2,+three:+3+},+function+(v)+{+return+v+*+3;+});。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|231238|请在此处查看交叉文档：http://jonathanpchen.com/underdash-api/#mapvalues-object-iteratee-identity|231239|entityMap|0|LINK|mutability|MUTABLE|url|http://jonathanpchen.com/underdash-api/#mapvalues-object-iteratee-identity^0|D|1E|1Z|22|0|B|22|0|0^^$0|@$1|2|3|4|5|6|7|P|8|@$9|Q|A|R|B|C]|$9|S|A|T|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|U|8|@]|D|@$9|V|A|W|1|X]]|E|$]]|$1|H|3|-4|5|6|7|Y|8|@]|D|@]|E|$]]]|I|$J|$5|K|L|M|E|$N|O]]]]

<p>You can use <code>_.mapValues(users, function(o) { return o.age; });</code> in Lodash and <code>_.mapObject({ one: 1, two: 2, three: 3 }, function (v) { return v * 3; });</code> in Underscore.</p>

<p>Check out the cross-documentation here: <a href="http://jonathanpchen.com/underdash-api/#mapvalues-object-iteratee-identity" rel="nofollow noreferrer">http://jonathanpchen.com/underdash-api/#mapvalues-object-iteratee-identity</a></p>


blocks|key|231260|text|我知道已经有很长一段时间了，但仍然缺少通过fold+(在js中也称为reduce+)的最明显的解决方案，为了完整起见，我将其留在这里：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|231261|function+mapO(f,+o)+{
++return+Object.keys(o).reduce((acc,+key)+=>+{
++++acc[key]+=+f(o[key])
++++return+acc
++},+{})
}|code-block|syntax|javascript|231262|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

<p>I know it's been a long time, but still the most obvious solution via fold (aka reduce in js) is missing, for the sake of completeness i'll leave it here:</p>

<pre><code>function mapO(f, o) {
  return Object.keys(o).reduce((acc, key) =&gt; {
    acc[key] = f(o[key])
    return acc
  }, {})
}
</code></pre>


blocks|key|14933|text|const+mapObject+=+(obj+=+{},+mapper)+=>
++Object.entries(obj).reduce(
++++(acc,+[key,+val])+=>+({+...acc,+[key]:+mapper(val)+}),
++++{},
++);|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|14934|unstyled|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|G|8|@]|9|@]|A|$B|C]]|$1|D|3|-4|5|E|7|H|8|@]|9|@]|A|$]]]|F|$]]

<pre><code>const mapObject = (obj = {}, mapper) =&gt;
  Object.entries(obj).reduce(
    (acc, [key, val]) =&gt; ({ ...acc, [key]: mapper(val) }),
    {},
  );
</code></pre>


blocks|key|14951|text|_.map使用类lodash循环来实现这一点|type|unstyled|depth|inlineStyleRanges|entityRanges|data|14952|+var+result={};
_.map({one:+1,+two:+2,+three:+3},+function(num,+key){+result[key]=num+*+3;+});
console.log(result)

//output
{one:+1,+two:+2,+three:+3}|code-block|syntax|javascript|14953|Reduce很聪明，看起来就像上面的答案|14954|_.reduce({one:+1,+two:+2,+three:+3},+function(result,+num,+key)+{
++result[key]=num+*+3
++return+result;
},+{});

//output
{one:+1,+two:+2,+three:+3}|14955|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

<p>_.map using lodash  like loop to achieve this</p>
<pre><code> var result={};
_.map({one: 1, two: 2, three: 3}, function(num, key){ result[key]=num * 3; });
console.log(result)

//output
{one: 1, two: 2, three: 3}
</code></pre>
<p>Reduce is clever looks like above answare</p>
<pre><code>_.reduce({one: 1, two: 2, three: 3}, function(result, num, key) {
  result[key]=num * 3
  return result;
}, {});

//output
{one: 1, two: 2, three: 3}
</code></pre>


<p>The <code>map</code> function in underscore.js, if called with a javascript object, returns an array of values mapped from the object's values.</p>

<pre><code>_.map({one: 1, two: 2, three: 3}, function(num, key){ return num * 3; });
=&gt; [3, 6, 9]
</code></pre>

<p>is there a way to make it preserve the keys? ie, I want a function that returns</p>

<pre><code>{one: 3, two: 6, three: 9}
</code></pre>


Map over object preserving keys

如果使用javascript对象调用underscore.js中的map函数，则会返回从对象的值映射而来的值数组。_.map({one: 1, two: 2, three: 3}, function(num, key){ return num * 3; });=> [3, 6, 9]有没有办法让它保留密钥？即，我想要一...

问在对象上映射保留关键字
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