typescript 如何根据数组项属性对打字稿数组中的值求和？
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How to sum values in typescript array based on array items property?
提问by Roxy'Pro
I'm working on small angular project. I have an array of receipt items, e.g. coke, fanta, pepsi, juice etc, with their prices and quantity of course.
我正在从事小型角度项目。我有一系列收据，例如可乐、芬达、百事可乐、果汁等，当然还有它们的价格和数量。
receiptItems: Array<ReceiptItem>;
This is how ReceiptItemlooks :
这是ReceiptItem看起来的样子：
export class ReceiptItem {
public id: string;
public product: Product;
public unitOfMeasure: UnitOfMeasure;
public discount: number;
public price: number;
public quantity: number;
public total: number;
public tax:Tax;
}
How can I in typescript get sum of total amount but only where property tax for example is equal to "25%"?
我怎样才能在打字稿中获得总金额，但只有在财产税等于“25%”的情况下？
In C# I remember I've used lambda expressions like this:
在 C# 中，我记得我使用过这样的 lambda 表达式：
IEnumerable<ReceiptItems> results = receiptItems.Where(s => s.Tax == "25.00");
totalSum = results.Sum(x => (x.TotalAmount));
How to achieve something similar in TypeScript / Angular?
如何在 TypeScript / Angular 中实现类似的功能？
回答by Suren Srapyan
Arrays in JavaScript/TypeScriptalso have these kind of methods. You can again filterwith you condition and then use reduceaggregation function to sum the items.
JavaScript/TypeScript 中的数组也有这些方法。您可以再次filter使用您的条件，然后使用reduce聚合函数对项目求和。
const sum = receiptItems.filter(item => item.tax === '25.00')
.reduce((sum, current) => sum + current.total, 0);
item.tax === '25.00'- this part you must adjust with your logic
item.tax === '25.00'- 这部分你必须根据你的逻辑进行调整
