JavaScript循环数组：比较前一个和下一个项。

huangapple
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英文:

JavaScript loop array: compare previous and next item

问题

  1. 循环数组并比较前一项和后一项。
  3. 我的数组:

const array = [{id: 1,name: 'A'},{id: 2,name: 'B'},{id: 3,name: 'B'},{id: 4,name: 'B'},{id: 5,name: 'C'},{id: 6,name: 'D'},{id: 7,name: 'E'},{id: 8,name: 'E'},{id: 9,name: 'E'}]

  2. 我的代码:

let result = []
array.forEach(function(item, index) {
if (index > 0) {
if (array[index].name == array[index - 1].name) {
result.push(array[index - 1].name)
}
}
});

console.log('result :', result); // 我得到的结果: [ 'B', 'B', 'E', 'E' ]

  2. 但我想要这个结果:

let result = [ 'B', 'B', 'B', 'E', 'E', 'E' ]

英文:

Loop array and compare the previous item and the next item.

My array:

  1. const array = [{id: 1,name: 'A'},{id: 2,name: 'B'},{id: 3,name: 'B'},{id: 4,name: 'B'},{id: 5,name: 'C'},{id: 6,name: 'D'},{id: 7,name: 'E'},{id: 8,name: 'E'},{id: 9,name: 'E'}]

My code:

  1. let result = []
  2. array.forEach(function(item, index) {
  3.     if (index > 0) {
  4.         if (array[index].name == array[index - 1].name) {
  5.             result.push(array[index - 1].name)
  6.         }
  7.     }
  8. });
  10. console.log('result :', result); // The result I got: [ 'B', 'B', 'E', 'E' ]

But I want this result:

  1. let result = [ 'B', 'B', 'B', 'E', 'E', 'E' ]

答案1

得分: 1

在这种情况下，reduce 是关键

  1. let result = array.reduce((acc, curr, index) => {
  2.   const previousItem = array[index - 1];
  3.   if (previousItem && curr.name === previousItem.name) {
  4.     acc.push(curr.name);
  5.   }
  6.   return acc;
  7. }, []);
  9. console.log(result); // 输出: [ 'B', 'B', 'B', 'E', 'E', 'E' ]
英文:

In such cases, reduce is the key

  1.  let result = array.reduce((acc, curr, index) => {
  2.  const previousItem = array[index - 1];
  3.  if (previousItem && curr.name === previousItem.name) {
  4.       acc.push(curr.name);
  5.  }
  6.  return acc;
  7.  }, []);
  9.  console.log(result); // Output: [ 'B', 'B', 'B', 'E', 'E', 'E' ]

答案2

得分: 1

你只需要有条件地检查前一个和后一个值。

  1. const array = [{id: 1, name: 'A'}, {id: 2, name: 'B'}, {id: 3, name: 'B'}, {id: 4, name: 'B'}, {id: 5, name: 'C'}, {id: 6, name: 'D'}, {id: 7, name: 'E'}, {id: 8, name: 'E'}, {id: 9, name: 'E'}]
  2. let result = [];
  4. array.forEach(function(item, index) {
  6.     let prev = index - 1; // Previous value
  7.     let next = index + 1; // Next value
  9.     if(index > 0) {
  10.         if((array[prev].name == array[index].name) || (array[index].name == array[next].name)) {
  11.             result.push(array[index].name)
  12.         }
  13.     }
  14. });
  16. console.log('result: ', result);
英文:

You just need to conditionally check the previous and next value.

  1. const array = [{id: 1,name: 'A'}, {id: 2,name: 'B'}, {id: 3,name: 'B'}, {id: 4,name: 'B'}, {id: 5,name: 'C'}, {id: 6,name: 'D'}, {id: 7,name: 'E'}, {id: 8,name: 'E'}, {id: 9,name: 'E'}]
  2.     let result = [];
  4.     array.forEach(function(item, index) {
  6.         let prev = index - 1; // Previous value
  7.         let next = index + 1; // Next value
  9.         if(index > 0) {
  10.             if((array[prev].name == array[index].name) || (array[index].name == array[next].name)) {
  11.                 result.push(array[index].name)
  12.             }
  13.         }
  14.     });
  16.     console.log('result: ', result);

答案3

得分: 0

  1. // 使用：
  3. <!-- 开始代码段: js 隐藏: false 控制台: true Babel: false -->
  5. <!-- 语言: lang-js -->
  7. const array = [
  8.   { id: 1, name: 'A' },
  9.   { id: 2, name: 'B' },
  10.   { id: 3, name: 'B' },
  11.   { id: 4, name: 'B' },
  12.   { id: 5, name: 'C' },
  13.   { id: 6, name: 'D' },
  14.   { id: 7, name: 'E' },
  15.   { id: 8, name: 'E' },
  16.   { id: 9, name: 'E' }
  17. ];
  19. const result = [];
  20. let prevName = null;
  21. let count = 0;
  23. array.forEach(item => {
  24.   if (item.name === prevName) {
  25.     count++;
  26.   } else {
  27.     if (count > 1) {
  28.       for (let i = 0; i < count; i++) {
  29.         result.push(prevName);
  30.       }
  31.     }
  32.     prevName = item.name;
  33.     count = 1;
  34.   }
  35. });
  37. if (count > 1) {
  38.   for (let i = 0; i < count; i++) {
  39.     result.push(prevName);
  40.   }
  41. }
  43. console.log('result:', result);
  45. <!-- 结束代码段 -->
英文:

Use:

<!-- begin snippet: js hide: false console: true babel: false -->

<!-- language: lang-js -->

  1. const array = [
  2. { id: 1, name: &#39;A&#39; },
  3. { id: 2, name: &#39;B&#39; },
  4. { id: 3, name: &#39;B&#39; },
  5. { id: 4, name: &#39;B&#39; },
  6. { id: 5, name: &#39;C&#39; },
  7. { id: 6, name: &#39;D&#39; },
  8. { id: 7, name: &#39;E&#39; },
  9. { id: 8, name: &#39;E&#39; },
  10. { id: 9, name: &#39;E&#39; }
  11. ];
  12. const result = [];
  13. let prevName = null;
  14. let count = 0;
  15. array.forEach(item =&gt; {
  16. if (item.name === prevName) {
  17. count++;
  18. } else {
  19. if (count &gt; 1) {
  20. for (let i = 0; i &lt; count; i++) {
  21. result.push(prevName);
  22. }
  23. }
  24. prevName = item.name;
  25. count = 1;
  26. }
  27. });
  28. if (count &gt; 1) {
  29. for (let i = 0; i &lt; count; i++) {
  30. result.push(prevName);
  31. }
  32. }
  33. console.log(&#39;result:&#39;, result);

<!-- end snippet -->

huangapple
  • 本文由 发表于 2023年5月30日 13:09:52
  • 转载请务必保留本文链接：https://go.coder-hub.com/76361753.html
  • arrays
  • compare
  • for-loop
  • javascript
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