JavaScript:如何对嵌套数组进行分组

const arr = [['apple', 'orange'], ['banana', 'pear'], ['grape', 'pineapple'], ['watermelon']];

const grouped = arr.reduce((result, subArr) => {
  subArr.forEach(item => {
    if (!result[item]) {
      result[item] = [];
    }
    result[item].push(subArr);
  });
  return result;
}, {});

console.log(grouped);

{
  'apple': [['apple', 'orange']],
  'orange': [['apple', 'orange']],
  'banana': [['banana', 'pear']],
  'pear': [['banana', 'pear']],
  'grape': [['grape', 'pineapple']],
  'pineapple': [['grape', 'pineapple']],
  'watermelon': [['watermelon']]
}

const arr = [['apple', 'orange'], ['banana', 'pear'], ['grape', 'pineapple'], ['watermelon']];

const grouped = new Map();

arr.forEach(subArr => {
  subArr.forEach(item => {
    if (!grouped.has(item)) {
      grouped.set(item, []);
    }
    grouped.get(item).push(subArr);
  });
});

console.log(Object.fromEntries(grouped));

{
  'apple': [['apple', 'orange']],
  'orange': [['apple', 'orange']],
  'banana': [['banana', 'pear']],
  'pear': [['banana', 'pear']],
  'grape': [['grape', 'pineapple']],
  'pineapple': [['grape', 'pineapple']],
  'watermelon': [['watermelon']]
}