array.map（）不返回单个数组

Question

I have the code below which I expect to map the result from the nested array and return a single array having both id's but I get 2 arrays instead. Can someone please guide me on what I'm doing wrongly?

 arrayVal = [{ sources: { data: [{ id: 1 }] } }, { sources: { data: [{ id: 2 }] } } ] for (let sub of arrayVal) { let result = sub.sources.data.map(x => (x.id)) console.log(result) } 

Answer 1

Right now, you're calling map for each element in arrayVal , so you get two arrays. Use reduce instead, to transform an array of objects into another array that's not necessarily one-to-one with the input elements:

 const arrayVal=[{sources:{data:[{id:1}]}},{sources:{data:[{id:2}]}}]; const result = arrayVal.reduce((a, { sources: { data } }) => ( [...a, ...data.map(({ id }) => id)] ), []); console.log(result) 

Answer 2

 arrayVal = [{ sources: { data: [{ id: 1 }] } }, { sources: { data: [{ id: 2 }] } } ] let result = []; for (let sub of arrayVal) { result = result.concat(sub.sources.data.map(x => (x.id))) } console.log(result) 

I think concat is what you were missing here, Hope this is what you trying to achieve

Answer 3

Try following

 var arrayVal = [{sources: {data: [{id: 1}]}},{sources: {data: [{id: 2}]}}]; // Create an array on sources.data and merge it into 1 collection (array) var result = arrayVal.reduce((a, c) => [...a, ...c.sources.data.map(({id}) => id)], []); console.log(result); 

For reference, Array.reduce

Also, you can improve your code as follows

 var arrayVal = [{sources: {data: [{id: 1}]}},{sources: {data: [{id: 2}]}}]; let result = []; for (let sub of arrayVal) { result.push(sub.sources.data.map(x => (x.id))); } console.log([].concat(...result)) 

Answer 4

Try this

 arrayVal = [{ sources: { data: [{ id: 1 }] } }, { sources: { data: [{ id: 2 }] } } ] let result = arrayVal.map((x) => x.sources.data[0].id) console.log(result) 

Answer 5

You can do something like this:

arrayVal = [{
    sources: {
      data: [{
        id: 1
      }]
    }
  },
  {
    sources: {
      data: [{
        id: 2
      }]
    }
  }
]

var flat = arrayVal.reduce(function(prev,curr,cI){
  prev.push(curr.sources.data.map(x => (x.id))[0]);
  return prev; // *********  Important ******
}, []);