Tag:aggregate

  • Set sorting in. Net can play like this, you know

    Time:2020-1-12

    Overview of C-SET types Collection is an important part of. Net FCL (Framework Class Library). All collection classes inherit from IEnumerable. Collection classes can be divided into the following categories: Association / non association type collection, sequential / random access collection, sequential / unordered collection, generic / non generic collection, thread safety collection. Bottom interface […]

  • A detailed explanation of the basic data structure of Python basic learning [numbers, strings, lists, tuples, sets, dictionaries]

    Time:2019-12-26

    This paper gives an example of the basic data structure of Python basic learning. To share with you for your reference, as follows: Preface Compared with PHP, Python is also a script parsing language, so when using python, variables and data structures are much simpler than compiled languages, butCompared with PHP, python has a strict […]

  • How to create and delete sets in mongodb

    Time:2019-12-3

    Create collection: createcollection() method MongoDB db.createCollection(name, options) Is used to create a collection Syntax:The basic createcollection() command syntax is as follows: db.createCollection(name, options) In the command, name is the name of the collection to be created. Options is a file that specifies the configured collection parameter type describe Name String Collection name to create Options […]

  • A tutorial of mongodb copying databases and collections between different hosts

    Time:2019-11-29

    1. db.cloneCollection() db.cloneCollection(from, collection, query)To copy data between different mongodb instances, db.clonecollection is an external embodiment of the clonecollection database command. function (from, collection, query) { assert( isString(from) && from.length ); assert( isString(collection) && collection.length ); collection = this._name + “.” + collection; query = query || {}; return this._dbCommand( { cloneCollection:collection, from:from, query:query } […]

  • JavaScript ES6 (V) – Collection

    Time:2019-11-18

    This article takes you to the beginning of JavaScript ES6 (5) – collection, reprint please indicate the source. In this chapter, we will learn the relevant usage and usage scenarios of set and weakset in ES6. I. overview Set set is a new built-in object type introduced by ES6. It has the same characteristics as […]

  • Spark operation aggregate, aggregate ByKey

    Time:2019-10-4

    1. aggregate function The elements in each partition are aggregated, and then the results and initial values of each partition are combined with the combine function. The final type returned by this function does not need to be the same as the element type in RDD. The seqOp operation aggregates the elements in each partition, […]

  • MongoDB aggregate uses a personal summary

    Time:2019-10-2

    Recently, I have been using mongodb. Sometimes I need to use statistics. I have checked some information on the Internet. The most suitable way to use aggregate is to use aggregate. Here is my experience in using it. MongoDB aggregationAggregate in MongoDB is mainly used to process data (such as statistical average, sum, etc.) and […]

  • Is the python collection a variable summary

    Time:2019-9-28

    A set is an unordered variable sequence. The elements in a collection must be hash-able, that is, immutable data types. Empty set a=set() Note that a={} creates an empty dictionary. Set — Variable sets. Elements in a collection can be added or deleted dynamically. Frozenset — an immutable set. Elements in a collection are immutable. […]

  • Redis hash and set-power node Java college collation

    Time:2019-8-14

    Redis hash values are a mapping between string fields and string values, so they are perfect data types representing objects in Redis and can store more than 40 billion key-value pairs. Example redis 127.0.0.1:6379> HMSET yiibai name “redis tutorial” description “redis basic commands for caching” likes 20 visitors 23000 OK redis 127.0.0.1:6379> HGETALL yiibai 1) […]

  • Collection Writing Guide in Ruby

    Time:2019-7-6

    Literal representations of inclined arrays and hashes (unless you need to pass parameters into their constructors). # bad arr = Array.new hash = Hash.new # good arr = [] hash = {} When you need an array of elements with no spaces or special symbols, you always use% w to define an array of strings. […]

  • The Elegant Posture of Processing Sets in Java 8-Stream

    Time:2019-5-26

    In Java, collections and arrays are the data structures that we often use. They need to be added, deleted, changed, checked, aggregated, counted, filtered and so on. By contrast, these operations are also available in relational databases, but before Java 8, the processing of collections and arrays was not very convenient. However, this problem has […]

  • A very useful Aggregate introductory tutorial in mongodb

    Time:2019-3-11

    Preface Aggregate translates to aggregate, but the experience of using it in practice is very much like the pipeline in linux. After each pipeline is processed, the result is handed over to the next pipeline. Your data is like water flow. Finally, you can get the data you want through each pipeline. What do we […]