How to filter array of object inside the array of the object type in JavaScript?-CodePudding

I'm facing one issue with one of the API responses, I have a response something like the below one.

[
  {type: "StateCountry", state: "AL", countries: [{type: "County", countyName: "US"}, {type: "County", countyName: "US"}, {type: "County", countyName: "US"}]},
  {type: "StateCountry", state: "AL", countries: [{type: "County", countyName: "German"}, {type: "County", countyName: "German"}, {type: "County", countyName: "German"}]},
  {type: "StateCountry", state: "AL", countries: [{type: "County", countyName: "Japan"}, {type: "County", countyName: "German"}, {type: "County", countyName: "German"}]},
]

it looks like an array of objects inside that have countries also the arrays of the object type. I need all the countyName in a single array for all the array of elements. like the below one type,

newNames = [US, German, Japan];

I tried something like this. but I couldn't able to get the output. can you please help me to do this? thank you all.

let newNames = this.selectedStateList.filter(item => item.countries.forEach(item => item.countries)).map(ele => ele.countries.forEach(item => item.countries))

CodePudding user response：

You can look through each countries object and add your data in a Set to get unique country.

const data = [ {type: "StateCountry", state: "AL", countries: [{type: "County", countyName: "US"}, {type: "County", countyName: "US"}, {type: "County", countyName: "US"}]}, {type: "StateCountry", state: "AL", countries: [{type: "County", countyName: "German"}, {type: "County", countyName: "German"}, {type: "County", countyName: "German"}]}, {type: "StateCountry", state: "AL", countries: [{type: "County", countyName: "Japan"}, {type: "County", countyName: "German"}, {type: "County", countyName: "German"}]}, ],
      result = Array.from(data.reduce((r, {countries}) => {
        countries.forEach(({countyName}) => r.add(countyName));
        return r;
      }, new Set()));
console.log(result);

CodePudding user response：

You need .maps, not .forEach - .maptransforms each element of an array, butforEach` does not return anything.

After getting an array of arrays of country names, you can flatten with .flat() - or you can put them together and use flatMap instead.

const input = [
  {type: "StateCountry", state: "AL", countries: [{type: "County", countyName: "US"}]},
  {type: "StateCountry", state: "AL", countries: [{type: "County", countyName: "German"}]},
  {type: "StateCountry", state: "AL", countries: [{type: "County", countyName: "Japan"}]},
];

const output = input.flatMap(
  obj => obj.countries.map(
    country => country.countyName
  )
);
console.log(output);

CodePudding user response：

Would something like this work?

const arr = [
  {type: "StateCountry", state: "AL", countries: [{type: "County", countyName: "US"}]},
  {type: "StateCountry", state: "AL", countries: [{type: "County", countyName: "German"}]},
  {type: "StateCountry", state: "AL", countries: [{type: "County", countyName: "Japan"}]}
]


const result = arr.reduce((acc,val)=>{
acc.push(val.countries[0].countyName)
return acc
},[] )

console.log(result)

CodePudding user response：

You could iterate over the given response (array of objects), then reference the countries element and get it's first entry as it is also an array of objects:

var input = [
    { type: "StateCountry", state: "AL", countries: [{ type: "County", countyName: "US" }] },
    { type: "StateCountry", state: "AL", countries: [{ type: "County", countyName: "German" }] },
    { type: "StateCountry", state: "AL", countries: [{ type: "County", countyName: "Japan" }] },
]
let output = []

for (const obj of input) {
    output.push(obj.countries[0].countyName)
}
console.log(output)