在Javascript

Question

使物體與數組的數組值。這是我的數組：

var input = [ 
    { 
     date: '2017-07-19', 
     number: 10 
    }, 
    { 
     date: '2017-07-20', 
     number: 7.5 
    }, 
    { 
     date: '2017-07-20', 
     number: 9 
    }, 
    { 
     date: '2017-07-21', 
     number: 8 
    }, 
    { 
     date: '2017-07-22', 
     number: 9.3 
    }, 
    { 
     date: '2017-07-22', 
     number: 6 
    }, 
    { 
     date: '2017-07-23', 
     number: 5.8 
    }, 
    { 
     date: '2017-07-23', 
     number: 7.2 
    }, 
    { 
     date: '2017-07-24', 
     number: 9 
    } 
]; 

這是我想完成

var output = [ 
    { 
     date: '2017-07-19', 
     number: [10], 
     average: 10 
    }, 
    { 
     date: '2017-07-20', 
     number: [10, 7.5, 9], 
     average: 8.8 
    }, 
    { 
     date: '2017-07-21', 
     number: [10, 7.5, 9, 8], 
     average: 8.6 
    }, 
    { 
     date: '2017-07-22', 
     number: [10, 7.5, 9, 8, 9.3, 6], 
     average: 8.3 
    }, 
    { 
     date: '2017-07-23', 
     number: [10, 7.5, 9, 8, 9.3, 6, 5.8, 7.2], 
     average: 7.9 
    }, 
    { 
     date: '2017-07-23', 
     number: [10, 7.5, 9, 8, 9.3, 6, 5.8, 7.2, 9], 
     average: 7.9 
    } 
]; 

到目前爲止，我只能添加號碼是什麼使用相同的日期並計算數字的平均值。我不知道如何製作var output陣列。 非常感謝您的幫助！

Answer 1

function group(arr) { 
 
    // FIRST PART: group the objects and sum their numbers 
 
    var indexHash = {};       // helps us check whether or not a date is encountered and at which index the object for that date is stored 
 
    var output = arr.reduce(function(acc, o) { // for each object o in the array 
 
     var ind = indexHash[o.date];    // get the index for this date from the index hash (if any) 
 
     if(ind) {         // if there is (there is already an object fro this date) 
 
      acc[ind].number.push(o.number);  // then push this object's number to its array of numbers 
 
      acc[ind].mean += o.number;   // add this object's number to it's mean (mean will serve as a sum for later when we will divide it by the length) 
 
     } 
 
     else          // otherwise (if we haven't store an object for this particular date) 
 
      indexHash[o.date] = acc.push({  // ... then store one 
 
       "date": o.date,     // that has its date equal to this object's date 
 
       "number": [o.number],    // and that has its number array containing this object's number 
 
       "mean": o.number     // and that has its mean initialized with this object's number 
 
      }) - 1; 
 
     return acc; 
 
    }, []); 
 
    
 
    // SECOND PART: sort the array by date (if not necessary then remove this bit of code) 
 
    output.sort(function(a, b) { 
 
     a = new Date(a.date).getTime();  
 
     b = new Date(b.date).getTime(); 
 
     return a - b; 
 
    }); 
 
    
 
    // THIRD PART: add the numbers of previous dates to the current date 
 
    var first = output.shift(), last = first;  // remove the first item of the array and store it (so we can get it back into the array later) and use it as the last seen object 
 
    output.forEach(function(o) {     // then for each object o 
 
     o.number = last.number.concat(o.number); // concat the last seen object's numbers to this object's number 
 
     o.mean += last.mean;      // add the sum of the last seen object's numbers to this object's sum 
 
     last = o;         // mark this object as the last seen object (so to add its numbers to the next object) 
 
    }); 
 
    output.unshift(first);      // get back the first object (previously removed) to the array 
 
    
 
    // FORTH PART: calculate the mean 
 
    output.forEach(function(o) { 
 
     o.mean /= o.number.length;    // the mean property of each object represents the sum of its number, to get the actual mean we have to divide the sum by the length of the number array 
 
    }); 
 
    
 
    return output; 
 
} 
 

 

 
var input = [{"date":"2017-07-19","number":10},{"date":"2017-07-20","number":7.5},{"date":"2017-07-20","number":9},{"date":"2017-07-21","number":8},{"date":"2017-07-22","number":9.3},{"date":"2017-07-22","number":6},{"date":"2017-07-23","number":5.8},{"date":"2017-07-23","number":7.2},{"date":"2017-07-24","number":9}]; 
 

 
console.log(group(input));

Answer 2

下面應該工作：

function mean(numbers) { 
 
    var sum = numbers.reduce(function(a, b) { return a + b; }); 
 
    return sum/numbers.length; 
 
} 
 

 
// Sort the input array by date 
 
input.sort(function(a, b) { 
 
      return new Date(a.date) - new Date(b.date); 
 
      }); 
 

 
// Add the first data-point to the output array 
 
var output = [{ date: input[0].date, 
 
       number: [input[0].number] }]; 
 

 
// Loop through the remaining input array elements 
 
for (var i=1; i<input.length; i++) { 
 

 
    var lastDate = output[output.length-1]; 
 

 
    if (input[i].date != lastDate.date) { 
 
    // This is a new date 
 
    // Calculate the average for the old date 
 
    lastDate.average = mean(lastDate.number); 
 

 
    // And create an output entry for the new date 
 
    output.push({ date: input[i].date, 
 
        number: lastDate.number.concat([input[i].number]) }); 
 
    // Set the number array to the previous date's number array with the newest number concatenated onto it 
 
    
 
    } else { 
 
    // If there is already an output entry for this date, then just add the new number 
 
    lastDate.number.push(input[i].number); 
 
    } 
 
} 
 

 
// Calculate average for last date 
 
lastDate = output[output.length-1]; 
 
lastDate.average = mean(lastDate.number); 
 

 
console.log(output);