reducers

问题 A Combiner runs after the Mapper and before the Reducer,it will receive as input all data emitted by the Mapper instances on a given node. then emits output to the Reducers. And also,If a reduce function is both commutative and associative , then it can be used as a Combiner. My Question is what does the phrase " commutative and associative " mean in this situation? 回答1: Assume you have a list of numbers, 1 2 3 4 5 6. Associative here means you can take your operation and apply it to any

问题 Haven't been able to find anything around here regarding this error: "Store does not have a valid reducer. Make sure the argument passed to combineReducers is an object whose values are reducers." My reducer export default function FriendListReducer(state = {friends : []}, action) { switch (action.type) { case 'ADD_FRIEND': return [ { friends : action.payload.friend }, ...state.friends ] default: return state; } return state; } Combiner import { combineReducers } from 'redux'; import {

问题 If I increase the number of mappers and decrease the number of reducers, then is there any difference in the performance (increase/decrease) of any job while execution? Also I want to ask that How to set the number of mappers and reducers? I have never played with this setting thats why I don't know about this. I know hadoop but I have code with it as I use Hive a lot. Also If I want to increase the number of mappers and reducers then how to set it and upto what value do I set it. Is it

问题 I'm currently learning React and I am trying to figure out how to use it with Redux for building a mobile app. I'm kind of confused on how the two are related/usable together. For example, I completed this tutorial in React https://www.raywenderlich.com/99473/introducing-react-native-building-apps-javascript, but now I want to play around with adding some reducers/actions to that app and I am not sure where those would tie in with what I've already done. 回答1: React is a UI framework that

问题 I have a todo list and want to set the state of that item in the array to "complete" if the user clicks on "complete". Here is my action: export function completeTodo(id) { return { type: "COMPLETE_TASK", completed: true, id } } Here is my reducer: case "COMPLETE_TASK": { return {...state, todos: [{ completed: action.completed }] } } The problem I'm having is the new state does no longer have the text associated of that todo item on the selected item and the ID is no longer there. Is this

问题 Is there a way to test a reduce class with MRUnit that uses MultipleOutputFormat to write to multiple output files? 回答1: It looks like support for MultipleOutputs is still work in progress in the MRUnit Jira. That being said, I found someone who implemented his own drivers subclassing MRUnit's MapReduceDriver to make it work with MultipleOutputs here, hope that helps. 回答2: MRUnit 1.1.0 has been released in June 2014 (see http://mrunit.apache.org/) This latest release includes support for

问题 I am new to the react-redux. I do have an object which is like, const initialState = { Low: [ { id: 0, technologyId: 0, technology: '', level: 'EASY' } ], Medium: [ { id: 0, technologyId: 0, technology: '', level: 'MEDIUM' } ], High: [ { id: 0, technologyId: 0, technology: '', level: 'TOUGH' } ] } Now, export default function QuizData(state = initialState, action) { switch (action.type) { case QUIZ_DATA: return { ...state, Low: action.data, error: false, } case RESET_SETUP_QUIZ: { console.log

问题 Using ngrx/redux, and following the ngrx example app as close as possible. Now I'm doing this somewhere in the application: get totalItems (): number { return sumBy(this._data.items, 'metadata.value'); } Where the _data is the raw async data from a remote server, and is part of some data of a User . Now I have some options: 1. Create a Class User constructor (public _data: UserResponse) {} And have some methods like: get name (): string { return this._data.name; } get address (): string {

问题 I have a reducer whereby I am retuning the appropriate state when an action is dispatched. Now I am calling an API at regular intervals so the result will trigger an action again and again. So what I want is that if the reducer state already has data then another reducer doesn't show the state as loading while the call is sent. It must maintain its loading state when receiving data the first time only. I hope I am able to explain it properly Here are my code snippets Loading state reducer

问题 This question already has an answer here : My Redux state has changed, why doesn't React trigger a re-render? (1 answer) Closed 2 years ago . I am trying to update a single chef within the chefs array in my redux state. An example of the array is as follows: [ { _id: 1, name: 'first chef' }, { _id: 2, name: 'second chef' }, { _id: 2, name: 'third chef' } ] I make a call to the API which then returns me the updated chef object. I basically find the related chef object in my current state,