如何统计API返回JSON数组中DeptName的出现次数并生成键值对？

Hey there! Let's break down how to count the occurrences of each DeptName in your array and output the result with lowercase keys, just like you want. Here are a couple of simple, effective ways to do this in JavaScript:

Method 1: Use reduce() (Clean & Concise) #

The reduce() method is perfect for accumulating values into an object—this is the most idiomatic approach for this kind of counting task:

const data = [ 
  {"id":"1939317721","pauseReason":"DISPLAY","DeptName":"Account"}, 
  {"id":"1939317722","pauseReason":"DISPLAY","DeptName":"Admission"}, 
  {"id":"1939317723","pauseReason":"DISPLAY","DeptName":"Account"}, 
  {"id":"1939317724","pauseReason":"DISPLAY","DeptName":"Account"}, 
];

const res = data.reduce((counts, item) => {
  // Convert DeptName to lowercase to match your expected output format
  const dept = item.DeptName.toLowerCase();
  // Increment the count: if the dept doesn't exist yet, default to 0 before adding 1
  counts[dept] = (counts[dept] || 0) + 1;
  return counts;
}, {}); // Start with an empty object to store counts

console.log(res); // Output: { account: 3, admission: 1 }

How this works: #

• We initialize reduce() with an empty object ({}) as the starting value for our counts.
• For each item in the array, we convert DeptName to lowercase to ensure consistent keys (since your desired result uses lowercase).
• We check if the department already exists in our counts object: if it does, we increment its value; if not, we set it to 1 (using (counts[dept] || 0) to handle the "first occurrence" case).

Method 2: Use forEach() (More Explicit for Beginners) #

If you prefer a more straightforward, step-by-step approach, a forEach() loop makes the counting logic easy to follow:

const data = [ 
  {"id":"1939317721","pauseReason":"DISPLAY","DeptName":"Account"}, 
  {"id":"1939317722","pauseReason":"DISPLAY","DeptName":"Admission"}, 
  {"id":"1939317723","pauseReason":"DISPLAY","DeptName":"Account"}, 
  {"id":"1939317724","pauseReason":"DISPLAY","DeptName":"Account"}, 
];

const res = {}; // Empty object to hold our counts

data.forEach(item => {
  const dept = item.DeptName.toLowerCase();
  // Check if the department is already in our counts object
  if (res[dept]) {
    res[dept]++; // Increment if it exists
  } else {
    res[dept] = 1; // Set to 1 if it's the first time we see it
  }
});

console.log(res); // Output: { account: 3, admission: 1 }

Bonus: Add Robustness (Handle Missing DeptName) #

If your array might contain items without a DeptName field, add a quick check to avoid errors:

// For reduce()
const res = data.reduce((counts, item) => {
  if (item.DeptName) { // Only process if the field exists
    const dept = item.DeptName.toLowerCase();
    counts[dept] = (counts[dept] || 0) + 1;
  }
  return counts;
}, {});

// For forEach()
data.forEach(item => {
  if (item.DeptName) {
    const dept = item.DeptName.toLowerCase();
    res[dept] = (res[dept] || 0) + 1;
  }
});

This ensures your code won't throw errors if any entries are missing the DeptName property.

内容的提问来源于stack exchange，提问作者shivani joshi