Lambda, filter, reduce and map Lambda Operator Some like it, others hate it and many are afraid of the lambda operator. We are confident that you will like it, when you have finished with this chapter of our tutorial. If not, you can learn all about
过滤查询以及聚合 A natural extension to aggregation scoping is filtering. Because the aggregation operates in the context of the query scope, any filter applied to the query will also apply to the aggregation. 过滤是聚合作用域的一个很自然的扩展.因为聚合工作在查询作用域的上下文中,那么适用于查询的任何过滤
1. lambda The lambda operator or lambda function is a way to create small anonymous functions , i.e. functions without a name. 可以方便的创造一个函数.比如 def add(x,y): return x+y 用lambda 写就是 lambda x,y:x+y 非常简洁.这条语句会返回一个函数指针,你可以他赋值,或者配合map ,reduce 等操作. 比如说想把list
public class map默认值 { public static void main(String[] args) { Map<String, String> resultMap = new HashMap(16); if (resultMap.isEmpty()) { System.out.println("map默认是空"); } if (resultMap != null) { System.out.println("map默认不是null"
做前端有多年了,看过不少技术文章,学了新的技术,但更新迭代快的大前端,庞大的知识库,很多学过就忘记了,特别在项目紧急的条件下,哪怕心中隐隐约约有学过一个方法,但会下意识的使用旧的方法去解决,多年前ES5几个新增的数组方法,好用但是常忘记用,趁着这周比较清闲,重温下并做下笔记,养成记笔记的好习惯. forEach map filter some every reduce reduceRight forEach forEach是ES5的Array方法中用得最频繁的一个,就是遍历,循环输出,它接受一个