How to get an objects out from very complex deeply nested array of objects and arrays?

Question

My data structure is very complex, can't figure out how to map through the data in a way so I can get what I want. There's a very big array with a lot of objects in it and each object has again arrays and objects nested in each other. The data looks like this:

const arr1 = [
  {
    id: 1,
    subject: 'Subject',
    chapters: [
      {
        name: 'chapter1',
        sections: [
          {
            name: 'section1',
            questions: [
              {
                title: 'Title',
                subtitle: 'SubTitle',
              },
              {
                title: 'Title',
                subtitle: 'SubTitle',
              },
            ],
          },
          {
            name: 'section2',
            questions: [
              {
                title: 'Title',
                subtitle: 'SubTitle',
              },
              {
                title: 'Title',
                subtitle: 'SubTitle',
              },
            ],
          },
        ],
      },
      {
        name: 'chapter2',
        sections: [
          {
            name: 'section1',
            questions: [
              {
                title: 'Title',
                subtitle: 'SubTitle',
              },
              {
                title: 'Title',
                subtitle: 'SubTitle',
              },
            ],
          },
          {
            name: 'section2',
            questions: [
              {
                title: 'Title',
                subtitle: 'SubTitle',
              },
              {
                title: 'Title',
                subtitle: 'SubTitle',
              },
            ],
          },
        ],
      },
    ],
  },
  {
    id: 2,
    subject: 'Subject',
    chapters: [
      {
        name: 'chapter1',
        sections: [
          {
            name: 'section1',
            questions: [
              {
                title: 'Title',
                subtitle: 'SubTitle',
              },
              {
                title: 'Title',
                subtitle: 'SubTitle',
              },
            ],
          },
          {
            name: 'section2',
            questions: [
              {
                title: 'Title',
                subtitle: 'SubTitle',
              },
              {
                title: 'Title',
                subtitle: 'SubTitle',
              },
            ],
          },
        ],
      },
      {
        name: 'chapter2',
        sections: [
          {
            name: 'section1',
            questions: [
              {
                title: 'Title',
                subtitle: 'SubTitle',
              },
              {
                title: 'Title',
                subtitle: 'SubTitle',
              },
            ],
          },
          {
            name: 'section2',
            questions: [
              {
                title: 'Title',
                subtitle: 'SubTitle',
              },
              {
                title: 'Title',
                subtitle: 'SubTitle',
              },
            ],
          },
        ],
      },
    ],
  },
];

How can I get an array from arr1 with only the objects located in 'questions' array, so it will look like this:

const arr2 = [
  {
    title: 'Title',
    subtitle: 'SubTitle',
  },
  {
    title: 'Title',
    subtitle: 'SubTitle',
  },
  {
    title: 'Title',
    subtitle: 'SubTitle',
  },
  {
    title: 'Title',
    subtitle: 'SubTitle',
  },
  {
    title: 'Title',
    subtitle: 'SubTitle',
  },
  {
    title: 'Title',
    subtitle: 'SubTitle',
  },
  {
    title: 'Title',
    subtitle: 'SubTitle',
  },
  {
    title: 'Title',
    subtitle: 'SubTitle',
  },
]

I think you will want to look into using something like lodash to help you: https://stackoverflow.com/questions/31054021/how-to-use-lodash-to-find-and-return-an-object-from-array — Colin Hale, Jul 12 '22 at 20:47
3 flatMaps for chapters sections and questions? . btw shouldnt it be 16 results in final? — cmgchess, Jul 12 '22 at 20:52

score 1 · Accepted Answer · answered Jul 12 '22 at 21:01

Use flatMap

const arr1 = [{id: 1,subject: 'Subject',chapters: [{name: 'chapter1',sections: [{name: 'section1',questions: [{title: 'Title',subtitle: 'SubTitle',},{title: 'Title',subtitle: 'SubTitle',},],},{name: 'section2',questions: [{title: 'Title',subtitle: 'SubTitle',},{title: 'Title',subtitle: 'SubTitle',},],},],},{name: 'chapter2',sections: [{name: 'section1',questions: [{title: 'Title',subtitle: 'SubTitle',},{title: 'Title',subtitle: 'SubTitle',},],},{name: 'section2',questions: [{title: 'Title',subtitle: 'SubTitle',},{title: 'Title',subtitle: 'SubTitle',},],},],},],},{id: 2,subject: 'Subject',chapters: [{name: 'chapter1',sections: [{name: 'section1',questions: [{title: 'Title',subtitle: 'SubTitle',},{title: 'Title',subtitle: 'SubTitle',},],},{name: 'section2',questions: [{title: 'Title',subtitle: 'SubTitle',},{title: 'Title',subtitle: 'SubTitle',},],},],},{name: 'chapter2',sections: [{name: 'section1',questions: [{title: 'Title',subtitle: 'SubTitle',},{title: 'Title',subtitle: 'SubTitle',},],},{name: 'section2',questions: [{title: 'Title',subtitle: 'SubTitle',},{title: 'Title',subtitle: 'SubTitle',},],},],},],},];

const result = arr1.flatMap(({chapters}) => 
    chapters.flatMap(({sections}) => 
        sections.flatMap(({questions}) => questions)
    )
);

console.log(result);

How to get an objects out from very complex deeply nested array of objects and arrays?

1 Answers1