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The first is the understanding of several operators related to map in RDD operator. map map is actually a mapping of data structures, which transforms one structure into another. A simple spark Program multiplies each number in the list by 2: object MapOperator { def main(args: Array[String]): Unit = { val conf = new SparkConf().s ...

Introduction to HashMap HashMap is a hash table that stores key value mappings.HashMap   The Map interface implementation based on hash table is one of the commonly used Java collections and is thread unsafe.HashMap   Null keys and values can be stored, but there can only be one null as a key and multiple null as a value.HashMap &nbs ...

HashMap class 1. HashMap class overview HashMap is the most frequently used implementation class of Map interface, which allows the use of null keys and null values. Like HashSet, the mapping order is not guaranteed. The Set composed of all keys is Set: unordered and non repeatable. Therefore, the class where the key is located sho ...

Map and Set Map and Set are two new data types in ES6Are built-in constructorsInstantiate using new Set It is used in conjunction with new const s = new Set() console.log(s) /* Set(0) {} [[Entries]] No properties size: (...) __proto__: Set */ Is a data set We can add data directly to the inside when ...

Reference link https://www.bilibili.com/video/BV1et411b73Z?p=264 Speech contest process management system Program requirements of speech contest Competition rules The school held a speech contest, in which 12 people participated. There are two rounds in the competition. The first round is the knockout and the second round is the finalEach ...

To generate a picture map, you can use ArcGIS, QGIS and other tools, or code. What I introduce here is, of course, implemented in code and using open source software. After all, there are too many introductions of desktop GIS tools, and everyone's maps are very beautiful. If you render a map in code, you have to mention GDAL and mapnik. GDAL i ...