reducers

问题 I was learning hadoop, I found number of reducers very confusing : 1) Number of reducers is same as number of partitions. 2) Number of reducers is 0.95 or 1.75 multiplied by (no. of nodes) * (no. of maximum containers per node). 3) Number of reducers is set by mapred.reduce.tasks . 4) Number of reducers is closest to: A multiple of the block size * A task time between 5 and 15 minutes * Creates the fewest files possible. I am very confused, Do we explicitly set number of reducers or it is

来源： https://stackoverflow.com/questions/59200785/react-usereducer-how-to-combine-multiple-reducers

问题 Code speaks better than language, so: ['a', 'b', 'c'].reduce((accumulator, value) => accumulator.concat(value), []); The code is very silly and returns a copied Array... TS complains on concat's argument: TS2345: Argument of type 'string' is not assignable to parameter of type 'ConcatArray'. 回答1: I believe this is because the type for [] is inferred to be never[] , which is the type for an array that MUST be empty. You can use a type cast to address this: ['a', 'b', 'c'].reduce((accumulator,

问题 how can i get asynchronous reducers data ,i search but didn't get solution Booking component cutPick = () => { this.props.pickup(false); } action creator export function pickup(latlng) { return function (dispatch) { dispatch({type:PICKUP_STATE,payload:latlng}); } } reducer import {PICKUP_STATE} from '../actions/types'; export default function (state={},action) { switch(action.type) { case PICKUP_STATE: return {...state,pickup:action.payload} } return state; } Map component import React from

问题 Overview (simplified): In my NodeJS server I've implemented the following GraphQL schema: type Item { name: String, value: Float } type Query { items(names: [String]!): [Item] } The client query then passes an array of names, as an argument: { items(names: ["total","active"] ) { name value } } The backend API queries a mysql DB, for the " total " and " active " fields (columns on my DB table) and reduces the response like so: [{"name":"total" , value:100} , {"name":"active" , value:50}] I

问题 Overview (simplified): In my NodeJS server I've implemented the following GraphQL schema: type Item { name: String, value: Float } type Query { items(names: [String]!): [Item] } The client query then passes an array of names, as an argument: { items(names: ["total","active"] ) { name value } } The backend API queries a mysql DB, for the " total " and " active " fields (columns on my DB table) and reduces the response like so: [{"name":"total" , value:100} , {"name":"active" , value:50}] I

问题 I have an application without redux, I handle the global state with hooks and the hook useReducer + context. I have 1 useReducer which makes like a Redux store. But to do this I can only send 1 reducer. In that reducer I have all the logic of the states, but I want to separate some functions of that reduce in other reducers. In redux there is the combineReducer to do this. But with hooks + context, how can I do this? How do I combine many reducers to send it to my Global Provider in the

问题 I don't understand what reduce-reducers is meant for. Should it be used in the case that I have 2 reducer functions containing the same action? function reducerA(state, action){ switch(action.type): ... case 'SAME_ACTION': {...state, field: state.field+1} } function reducerB(state, action){ switch(action.type): ... case 'SAME_ACTION': {...state, field: state.field*2} } So if I call reduceReducer on reducerA and reducerB and action 'SAME_ACTION' is invoked for {field: 0} then I would have a

问题 Below are my action and reducer files - In my component state I am only seeing this.props.mainData - but others subdataOneData etc., are not being loaded in to the state - till reducer i see the right actions are being dispatched and I also see the data for sub - calls - but they are not reaching my component - I have mapStatetoprops - where I am doing New issue: as per the updated code - when i print out payload in reducer - I see maindata with the api data but SubData [{}, {}, {}] ..?

问题 In many MapReduce programs, I see a reducer being used as a combiner as well. I know this is because of the specific nature of those programs. But I am wondering if they can be different. 回答1: Yes, a combiner can be different to the Reducer, although your Combiner will still be implementing the Reducer interface. Combiners can only be used in specific cases which are going to be job dependent. The Combiner will operate like a Reducer, but only on the subset of the Key/Values output from each