reduce

问题 So, I saw someone using the reduce method to calculate the Fibonacci sequence. Here is his idea: (1,0) , (1,1) , (2,1) , (3,2) , (5,3) corresponds to 1, 1, 2, 3, 5, 8, 13, 21 ....... and the code looks like this def fib_reduce(n): initial =(1,0) dummy = range(n) fib_n = reduce(lambda prev ,b : (prev[0] + prev[1], prev[0]), dummy, initial) return fib_n[0] I understand the (prev[0] + prev[1] , prev[0]) which is like a, b = b, b + a . However, I don't understand what this b stands for ? May

问题 const arr = [5,6,0,7,8]; const sum = (arr,num) => arr.reduce((total)=>(num==0 ? total : total+num), 0) console.log(sum(arr, 0)) Please check how can I make it work. Did some mistake but don't know what exactly. Output is a function instead of a result. 回答1: This is awkward to do in .reduce because it goes through the entire array. If we do a naive implementation you can see the problem: const arr = [5,6,0,7,8]; const sum = (arr,num) => arr.reduce((total, x)=>(num==x ? total : total+x), 0)

问题 I have been trying to create an example problem for testing out the reduce function in javascript. the program it is intended to a single object from a set of input lines. function generateInputs(){ var inputLines = Math.floor(Math.random() * 100) var arr = []; arr[0] = inputLines; var userIDs = ["a","b","c","d","e"] for(i=0; i<inputLines; i++){ let userID = userIDs[Math.floor(Math.random() * userIDs.length)] let usage = Math.floor(Math.random(600)) arr.push(userID + " " + usage) } return arr

问题 I want to return an array grouped by the team with gp, win, loss summed up. I'm trying to accomplish this with reduce, however, the totals are not adding up. Here's my code... const myArr = [ {team: 'Red', gp: 3, win:2, loss:1}, {team: 'Black', gp: 3, win:1, loss:2}, {team: 'Red', gp: 10, win:8, loss:2} ] let output = myArr.reduce( (acc, curr) => { acc[curr.team] = { gp: acc.gp + curr.gp, win: acc.win + curr.win, loss: acc.loss + curr.loss }; return acc; }, { gp: 0, win: 0, loss: 0 } );

问题 Assume List<int> diff(List<int> a, List<int> b) { // assume same length lists List<int> diff= new List<int>(a.Count); for (int i=0; i<diff.Count; ++i) { diff[i] = a[i] - b[i]; } return diff; } I would like to have some kind of one-liner do the same, or something that uses a lambda, rather than re-writing all the boilerplate. for instance, in python, this would be either [ai-bi for ai,bi in zip(a,b)] or even np.array(a) - np.array(b) Is there a nice way to write this in C#? All my searches

问题 Consider something like this: typedef struct TS { double a,b,c; } S; ... S x,y; ... MPI_Allreduce(&x, &y, 3, MPI_DOUBLE, MPI_SUM, MPI_COMM_WORLD); Is the above code completely portable (without using MPI_Type_struct and all; all variables in the structure are assumed to be of the same type)? Also in the case when different hardware on various nodes is used? Thanks in advance, Jac 回答1: Hristo Iliev's completely right; the C standard allows arbitrary padding between the fields. So there's no

问题 In Hive I ofter do queries like: select columnA, sum(columnB) from ... group by ... I read some mapreduce example and one reducer can only produce one key. It seems the number of reducers completely depends on number of keys in columnA. Therefore, why could hive set number of reducers manully? If there are 10 different values in columnA and I set number of reducers to 2 , what will happen? Each reducers will be reused 5 times? If there are 10 different values in columnA and I set number of

问题 In Hive I ofter do queries like: select columnA, sum(columnB) from ... group by ... I read some mapreduce example and one reducer can only produce one key. It seems the number of reducers completely depends on number of keys in columnA. Therefore, why could hive set number of reducers manully? If there are 10 different values in columnA and I set number of reducers to 2 , what will happen? Each reducers will be reused 5 times? If there are 10 different values in columnA and I set number of

问题 I am looking at precipitation data (both GPM and CHIRPS) for different provinces in Indonesia using Google Earth Engine. GPM is sub-daily (every 30 minutes) and CHIRPS is daily. I am only interested in getting the monthly values. Unlike here and here I am not interested in getting the multi-annual monthly values, but simply the average of each month and make a time series. Here I found a way to create a list of values containing the mean of each month. Edit: Thanks to Nicholas Clinton's

问题 I am looking at precipitation data (both GPM and CHIRPS) for different provinces in Indonesia using Google Earth Engine. GPM is sub-daily (every 30 minutes) and CHIRPS is daily. I am only interested in getting the monthly values. Unlike here and here I am not interested in getting the multi-annual monthly values, but simply the average of each month and make a time series. Here I found a way to create a list of values containing the mean of each month. Edit: Thanks to Nicholas Clinton's