javascript 带下划线的 Map Reducing 对象
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Map Reducing object with underscore
提问by vincewilfork
I want to reduce this object to just an object containing product name and average price. What's the fastest way to do it?
我想将此对象减少为仅包含产品名称和平均价格的对象。最快的方法是什么？
var foo = { group1: [
{
name: "one",
price: 100
},
{
name: "two",
price: 100
}],
group2: [
{
name: "one",
price: 200
},
{
name: "two",
price: 200
}],
group3: [
{
name: "one",
price: 300
},
{
name: "two",
price: 300
}]
}
resulting in
导致
var foo2 = [{
name: 'one',
price: 200
},{
name: 'two',
price: 200
}];
Thanks!
谢谢！
采纳答案by Evan
Edit: Leaving this up for now, but I totally forgot about _.flatten, so redmallard's got a much better answer.
编辑：暂时搁置这个，但我完全忘记了 _.flatten，所以 redmallard 得到了更好的答案。
If you already know the product names and they appear in every group, you could do the whole thing quickly this way:
如果您已经知道产品名称并且它们出现在每个组中，那么您可以通过以下方式快速完成整个操作：
var productAveragePrices = function ( groups, names ) {
return _.map( names, function ( name ) {
var product = { name: name }, productPricesSum = 0;
_.each( groups, function ( group ) {
productPricesSum += ( _.findWhere( group, product ).price );
});
product.price = productPricesSum / _.size( groups );
return product;
});
};
var foo2 = productAveragePrices = function ( foo, ['one', 'two'] );
I put this together, which should work even if your groups have different products (eg "one" in first, second, and fourth group and "two" in first and third):
我把它们放在一起，即使您的团队有不同的产品（例如，第一、第二和第四组中的“一个”和第一和第三组中的“两个”）也应该有效：
var productPriceReducer = function( memo, group ) {
_.each( group, function( product ) {
// Grabs the current product from the list we're compiling
var memoProduct = _.findWhere( memo, { name: product.name });
if ( !memoProduct ) {
// If the product doesn't exist, creates a holder for it and its prices
memoProduct = {
name: product.name,
prices: [ product.price ]
};
memo.push( memoProduct );
} else {
// Otherwise, it just adds the prices to the existing holder.
memoProduct.prices.push( product.price );
}
});
return memo;
};
// This gets us a list of products with all of their prices across groups
var productPrices = _.reduce( foo, productPriceReducer, [] );
// Then reducing to the average is pretty simple!
var productAveragePrices = _.map( productPrices, function ( product ) {
var sumPrices = _.reduce( product.prices, function ( memo, price ) {
return memo + price;
}, 0 );
return {
name: product.name,
price: sumPrices / product.prices.length
};
});
You could still do the above in one function with a counter and summing the prices, but this way, you also have the prices in case you want to, say, take the standard deviation or find the mode.
您仍然可以使用计数器在一个函数中执行上述操作并对价格求和，但是这样，您也可以拥有价格，以防万一，例如，采用标准偏差或找到模式。
回答by redmallard
Not to rain on Evan's parade, but here's an alternative that is a bit shorter ;)
不要在埃文的游行中下雨，但这里有一个更短的替代方案；)
result = _.chain(original)
.flatten()
.groupBy(function(value) { return value.name; })
.map(function(value, key) {
var sum = _.reduce(value, function(memo, val) { return memo + val.price; }, 0);
return {name: key, price: sum / value.length};
})
.value();
See it in action: http://plnkr.co/edit/lcmZoLkrlfoV8CGN4Pun?p=preview
回答by user239558
I really like redmallard's solution, but I wanted to golf a little.
我真的很喜欢 redmallard 的解决方案，但我想打一点高尔夫球。
Underscore doesn't include a sumfunction, but we can write pretty elegant functional expressions by adding a summixin. This function is known as addin the underscore-contribs repo.
Underscore 不包含sum函数，但我们可以通过添加一个summixin来编写非常优雅的函数表达式。此函数在 underscore-contribs 存储库中称为add。
Then we can write:
然后我们可以写：
// Somewhere in the initialization of the program
_.mixin({
sum : function (arr) {
return _.reduce(arr, function (s, x) { return s + x;}, 0);
}
});
result = _.chain(original)
.flatten()
.groupBy('name') // shorthand notation
.map(function (value, key) {
var sum = _.chain(value).pluck('price').sum().value();
return { name: key, price: sum / value.length};
})
.value();
http://plnkr.co/edit/ul3odB7lr8qwgVIDOtM9
http://plnkr.co/edit/ul3odB7lr8qwgVIDOtM9
But then we can also create an avgmixin to expand our toolbelt:
但是我们也可以创建一个avgmixin 来扩展我们的工具带：
// Somewhere in the initialization of the program
_.mixin({
sum : function (arr) {
return _.reduce(arr, function (s, x) { return s + x;}, 0);
},
avg : function (arr) {
return _.sum(arr)/arr.length;
}
});
result = _.chain(original)
.flatten()
.groupBy('name') // shorthand notation
.map(function (value, key) {
return { name: key, price: _.avg(value)};
})
.value();
