JS get all the arrays within an array

Question

I have an object that looks like the following:

const test = {
  leagues: [
    {
      timezone: "GMT",
      date: "1/2/2",
      premierLeague: [
        { name: "Liverpool", age: 1892 },
        { name: "Manchester Utd", age: 1878 }
      ],
      laLiga: [
        {
          team: "Real Madrid",
          stadium: "Bernabeu"
        },
        {
          team: "Barcelona",
          stadium: "Camp Nou"
        }
      ]
    }
  ]
};

and I want the result to look like

const result = [
  { name: "Liverpool", age: 1892 },
  { name: "Manchester Utd", age: 1878 },
  {
    team: "Real Madrid",
    stadium: "Bernabeu"
  },
  {
    team: "Barcelona",
    stadium: "Camp Nou"
  }
];

I have tried to use flat() but am having trouble getting the arrays within the leagues. The result will be dynamic so I need to be able to get all the arrays within leagues. Can anyone point me in the correct direction to do this?

Do you really want that result? It's objects of totally different shapes in the same array. Don't do that. — Bergi
– Bergi, Commented May 9, 2022 at 20:19
Check the solutions here, it may help stackoverflow.com/questions/27266550/… — Evren
– Evren, Commented May 9, 2022 at 20:20
@Evren Not sure how that can help, please be more specific how you think it will help — Ruan Mendes
– Ruan Mendes, Commented May 9, 2022 at 20:21

Jared Smith · Accepted Answer · 2022-05-09 20:47:12Z

3

If your object structure doesn't go an deeper than that, this long one-liner should work:

const result = test.leagues.reduce((arr, obj) => Object.values(val).reduce((innerArr, val) => Array.isArray(val) ? innerArr.concat(val) : innerArr, arr), []);

Somewhat ungolfed:

const result = test.leagues.reduce((arr, obj) => {
  return Object.values(val).reduce((innerArr, val) => {
    return Array.isArray(val)
      ? innerArr.concat(val) 
      : innerArr
  }, arr);
}), []);

edited May 9, 2022 at 20:47

answered May 9, 2022 at 20:23

Jared Smith

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5 Comments

Bergi Over a year ago

Mixing reduce with forEach and push is quite ugly, don't you think?

Jared Smith Over a year ago

@Bergi you're not wrong. I fired that off between meetings

Bergi Over a year ago

Thanks! I'd still prefer @Juan's for+push or my flatMap over reduce, but at least it's consistent now :-)

Ruan Mendes Over a year ago

I almost deleted my answer since I saw this and @Bergi's . I still posted it in because the double loop is the easiest one to scan and quickly know what is happening. I do know it is not as elegant 😊

Jared Smith Over a year ago

@JuanMendes don't sweat it. Elegant is a matter of degrees.

peter flanagan · Accepted Answer · 2022-05-10 07:42:47Z

2

You might be looking for

const result = test.leagues.flatMap(league =>
  Object.values(league).filter(Array.isArray).flat()
);

edited May 10, 2022 at 7:42

peter flanagan

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answered May 9, 2022 at 20:25

Bergi

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2 Comments

peter flanagan Over a year ago

thanks for this, but as I said the response will be dynamic so can't hard code names of the arrays

Bergi Over a year ago

@peterflanagan Oh I thought you would know the structure, and only the values in the arrays would be dynamic… but if you don't know the names of array-valued properties I have updated my answer. It still assumes test.leagues to be an array of objects with possibly-array-valued properties, is that right? Not arbitrarily nested?

Ruan Mendes · Accepted Answer · 2022-05-10 14:58:16Z

1

This sounds weird, you'll end up with objects of different shapes in the same array. I'm not sure how you'll deal with that.

It looks like you're trying to concatenate every value of test.leagues that is itself an array.

const test = {
  leagues: [{
    timezone: "GMT",
    date: "1/2/2",
    premierLeague: [{
        name: "Liverpool",
        age: 1892
      },
      {
        name: "Manchester Utd",
        age: 1878
      }
    ],
    laLiga: [{
        team: "Real Madrid",
        stadium: "Bernabeu"
      },
      {
        team: "Barcelona",
        stadium: "Camp Nou"
      }
    ]
  }]
};


const output = [];
for (const league of test.leagues) {
  for (const key in league) {
    if (Array.isArray(league[key])) {
      // Push each element in `league[key]` onto `output`
      // so we don't have to flatten it later
      output.push(...league[key]);
    }
  }
}
console.log({
  output
});

edited May 10, 2022 at 14:58

answered May 9, 2022 at 20:26

Ruan Mendes

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2 Comments

peter flanagan Over a year ago

this isn't actually what I want. It should be a flat array

Ruan Mendes Over a year ago

@peterflanagan Fixed by spreading the arrays as we push them: output.push(...league[key]);

Jose A · Accepted Answer · 2022-05-09 20:30:24Z

Well, I'm also adding my 2 cents over here. I do agree with everyone else. See if this works:

const test = {
  leagues: [
    {
      timezone: "GMT",
      date: "1/2/2",
      premierLeague: [
        { name: "Liverpool", age: 1892 },
        { name: "Manchester Utd", age: 1878 }
      ],
      laLiga: [
        {
          team: "Real Madrid",
          stadium: "Bernabeu"
        },
        {
          team: "Barcelona",
          stadium: "Camp Nou"
        }
      ]
    }
  ]
};

let finalArray = [];

function recursiveArr(obj, arrayToPush) {
    for(const [key, val] of Object.entries(obj)) {
    if(Array.isArray(obj[key])) {
      arrayToPush.push(obj[key]);
      continue;
    }
    
    const type = typeof obj[key];
    
    if(type === "object") {
       recursiveArr(obj[key], arrayToPush);
    }
  }
}

recursiveArr(test.leagues, finalArray);

console.log(finalArray.flat())

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