PHP合并首元素相同的数组元素并累加第二个元素

Got it, let's solve this problem where you need to merge entries in your array that share the same date, then sum up their corresponding visit counts. This is a super common data aggregation task, and here are a couple of clean, practical ways to do it in JavaScript:

Method 1: Use Array.reduce() (Most Concise) #

This is the go-to approach for this kind of data transformation—it lets you iterate through the array once and build up your aggregated result as you go.

const rawData = [["Apr 6",1],["Apr 6",1],["Apr 6",1],["Apr 6",1],["Apr 6",1],["Apr 6",1],["Apr 6",1],["Apr 6",1],["Apr 6",1],["Apr 6",1],["Apr 6",1],["Apr 6",1],["Apr 7",1],["Apr 7",1],["Apr 7",1],["Apr 13",1],["Apr 14",1],["Apr 15",1],["Apr 15",1],["Apr 15",1],["Apr 16",1],["Apr 16",1],["Apr 16",1],["Apr 16",1],["Apr 16",1],["Apr 16",1],["Apr 16",1],["Apr 17",1],["Apr 17",1],["Apr 17",1]];

const aggregatedData = Object.entries(
  rawData.reduce((acc, [date, count]) => {
    // If the date already exists in the accumulator, add the count; otherwise set it
    acc[date] = (acc[date] || 0) + count;
    return acc;
  }, {})
);

console.log(aggregatedData);
// Output: [["Apr 6",12], ["Apr 7",3], ["Apr 13",1], ["Apr 14",1], ["Apr 15",3], ["Apr 16",7], ["Apr 17",3]]

How this works: #

• We start with an empty object ({}) as our accumulator (acc).
• For each entry in rawData, we destructure the date and count.
• We check if the date is already a key in the accumulator: if yes, we add the current count to the existing value; if not, we set it to the current count (falling back to 0 if it doesn't exist).
• Finally, we use Object.entries() to convert the accumulator object back into the array format you need.

Method 2: Use a Loop (More Explicit for Beginners) #

If you prefer a more step-by-step approach that's easier to follow at first, a simple for loop works great too:

const rawData = [["Apr 6",1],["Apr 6",1],["Apr 6",1],["Apr 6",1],["Apr 6",1],["Apr 6",1],["Apr 6",1],["Apr 6",1],["Apr 6",1],["Apr 6",1],["Apr 6",1],["Apr 6",1],["Apr 7",1],["Apr 7",1],["Apr 7",1],["Apr 13",1],["Apr 14",1],["Apr 15",1],["Apr 15",1],["Apr 15",1],["Apr 16",1],["Apr 16",1],["Apr 16",1],["Apr 16",1],["Apr 16",1],["Apr 16",1],["Apr 16",1],["Apr 17",1],["Apr 17",1],["Apr 17",1]];

const tempObj = {};

// Loop through each entry to build the aggregated object
for (const [date, count] of rawData) {
  if (tempObj[date]) {
    tempObj[date] += count;
  } else {
    tempObj[date] = count;
  }
}

// Convert the object back to the desired array format
const aggregatedData = Object.entries(tempObj);

console.log(aggregatedData);
// Same output as above

Both methods will give you exactly what you need: a condensed array where each unique date is paired with the total number of visits on that day.

内容的提问来源于stack exchange，提问作者Zach Handley