Using Object key to make up a array

Question

Considering follow code

const filterArray = ['a', 'b']
const objectToBeFilter = {
  a: {
    ab: 'ab',
    ac: 'ac',
    ad: 'ad'
  },
  b: {
    bb: 'bb',
    bc: 'bc',
    bd: 'bd'
  },
  c: {
    cb: 'cb',
    cc: 'cc',
    cd: 'cd'
  }
}

const resultWantToGet = [
  a: {
    ab: 'ab',
    ac: 'ac',
    ad: 'ad'
  },
  b: {
    bb: 'bb',
    bc: 'bc',
    bd: 'bd'
  }
]

FilterArray is a array to be used as a filter index, objectToBeFilter is a object which I want to handle. How to use filterArray to filter objectToBeFilter and then convert it to a array resultWantToGet?

You say you want an array, but the "array" you are showing has keys a and b, which is a syntax error. Do you want an array or new object? — Mark
– Mark, Commented Sep 17, 2018 at 3:39
The resultWantToGet is a array contain many objects, doesn't it? — ccd
– ccd, Commented Sep 17, 2018 at 4:10
No, @yuanlai, an array of objects will look like this: [ { ab: 'ab', ac: 'ac', ad: 'ad' }, { bb: 'bb', bc: 'bc', bd: 'bd' } ] (without the keys). See answer below if that's what you are looking for. — Mark
– Mark, Commented Sep 17, 2018 at 4:26

Mark · Accepted Answer · 2018-09-17 04:24:37Z

1

Based on your last comment, it seem like you want an array of objects. You can do this simply with, which will give you the objects from objectToBeFilter keyed at a and b in an array:

const filterArray = ['a', 'b']
const objectToBeFilter = {
  a: {
    ab: 'ab',
    ac: 'ac',
    ad: 'ad'
  },
  b: {
    bb: 'bb',
    bc: 'bc',
    bd: 'bd'
  },
  c: {
    cb: 'cb',
    cc: 'cc',
    cd: 'cd'
  }
}


let result = filterArray.map(key => objectToBeFilter[key])
console.log(result)

This looks different than your expected result because arrays don't have keys. If you want each item to be identified with a key, you probably want an object, but if you want an ordered collection, then an array is appropriate.

answered Sep 17, 2018 at 4:24

Mark

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Comments

CertainPerformance · Accepted Answer · 2018-09-17 03:37:55Z

You can map by filterArray and spread into a new object:

const filterArray = ['a', 'b']
const objectToBeFilter = {
  a: {
    ab: 'ab',
    ac: 'ac',
    ad: 'ad'
  },
  b: {
    bb: 'bb',
    bc: 'bc',
    bd: 'bd'
  },
  c: {
    cb: 'cb',
    cc: 'cc',
    cd: 'cd'
  }
};
console.log({
  ...filterArray.map(key => ({ [key]: objectToBeFilter[key] }))
});

Or, if you don't want to create intermediate objects, use reduce:

const filterArray = ['a', 'b']
const objectToBeFilter = {
  a: {
    ab: 'ab',
    ac: 'ac',
    ad: 'ad'
  },
  b: {
    bb: 'bb',
    bc: 'bc',
    bd: 'bd'
  },
  c: {
    cb: 'cb',
    cc: 'cc',
    cd: 'cd'
  }
};
console.log(filterArray.reduce((a, prop) => {
  a[prop] = objectToBeFilter[prop];
  return a;
}, {}));

Eddie · Accepted Answer · 2018-09-17 03:39:11Z

1

You can use reduce to loop and construct new object.

const filterArray = ['a', 'b']
const objectToBeFilter = {
  a: {
    ab: 'ab',
    ac: 'ac',
    ad: 'ad'
  },
  b: {
    bb: 'bb',
    bc: 'bc',
    bd: 'bd'
  },
  c: {
    cb: 'cb',
    cc: 'cc',
    cd: 'cd'
  }
}

const resultWantToGet = filterArray.reduce((c, v) => {
  if (objectToBeFilter[v]) c[v] = objectToBeFilter[v]; //Check if the key exist in objectToBeFilter, if it does, assign to the accumulator. 
  return c;
}, {})

console.log(resultWantToGet);

answered Sep 17, 2018 at 3:39

Eddie

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4 Comments

ccd Over a year ago

Sorry for disturbing, how to convert resultWantToGet to a array?

Eddie Over a year ago

@yuanlai, You need numerical indices?

ccd Over a year ago

Because I want to use length and resultWantToGet[index] like method, so I have this idea.

Eddie Over a year ago

You can use Object.values to get all values. If you want to get the length:Object.values(resultWantToGet).length

Ahmed Yousif · Accepted Answer · 2018-09-17 04:19:00Z

1

you can use the following code Object.keys(objectToBeFilter) get list of filtered object keys then filter keys that included in filter array .filter(key => filterArray.includes(key)) then construct a new object with only the filtered properties reduce((obj, key)

const filterArray = ['a', 'b']
const objectToBeFilter = {
  a: {
    ab: 'ab',
    ac: 'ac',
    ad: 'ad'
  },
  b: {
    bb: 'bb',
    bc: 'bc',
    bd: 'bd'
  },
  c: {
    cb: 'cb',
    cc: 'cc',
    cd: 'cd'
  }
}

const resultWantToGet =  Object.keys(objectToBeFilter)
  .filter(key => filterArray.includes(key))
  .reduce((obj, key) => {
    obj[key] = objectToBeFilter[key];
    return obj;}, {});

console.log(resultWantToGet)

edited Sep 17, 2018 at 4:19

answered Sep 17, 2018 at 4:13

Ahmed Yousif

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