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: stackoverflow.com/questions/31054021/… — Colin Hale
– Colin Hale, Commented Jul 12, 2022 at 20:47
3 flatMaps for chapters sections and questions? . btw shouldnt it be 16 results in final? — cmgchess
– cmgchess, Commented Jul 12, 2022 at 20:52

trincot · Accepted Answer · 2022-07-12 21:01:33Z

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);

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