Return new array with specific values using map()-CodePudding

Please help me with a solution to extract in a new array only the specific object that has the paramenter checked: true. See the example below:

    {nodeName: 'node1', nodeId: 1, checked: false },
    {nodeName: 'node2', nodeId: 2, checked: true },
    {nodeName: 'node3', nodeId: 3, checked: false },
    {nodeName: 'node4', nodeId: 4, checked: true },
    {nodeName: 'node5', nodeId: 5, checked: false },
    {nodeName: 'node6', nodeId: 6, checked: true },
]

let checkedNodes = nodes.map(node => {
    let options = {
        "name": node.nodeName,
        "id": node.nodeId,
        "checked": node.checked
    }
    
    return options;
})

This will return all the nodes :(
How can I make the verification, in order to return the array like this?

[
    {
        "name": "node2",
        "id": 2,
        "checked": true
    },
    {
        "name": "node4",
        "id": 4,
        "checked": true
    },
    {
        "name": "node6",
        "id": 6,
        "checked": true
    }
]

CodePudding user response：

Map is inappropriate for this task - it is used to take a list of inputs and to produce an output for each input (see documentation).

You want to use find (for one result or undefined) or filter (for an array of 0 or or more matching objects).

// Find the first checked node, or undefined if none are checked
const checkedNodes = nodes.find(node => node.checked);

// Find all checked nodes
const checkedNodes = nodes.filter(node => node.checked);

CodePudding user response：

You can't do this with just .map(). .map() will always return an array the same exact size of the input array.

You can either .filter() the array then .map(), or use .reduce().

In this case, .filter() is going to be the easiest, both to read and write. Just include it before the .map() call:

const nodes = [
  {nodeName: 'node1', nodeId: 1, checked: false },
  {nodeName: 'node2', nodeId: 2, checked: true },
  {nodeName: 'node3', nodeId: 3, checked: false },
  {nodeName: 'node4', nodeId: 4, checked: true },
  {nodeName: 'node5', nodeId: 5, checked: false },
  {nodeName: 'node6', nodeId: 6, checked: true },
]

const checkedNodes = nodes
  .filter(node => node.checked)
  .map(node => ({
    name: node.nodeName,
    id: node.nodeId,
    checked: node.checked
  }));
  
console.log(checkedNodes);

The only downside to this approach is it'll iterate over your list possibly twice, which is fine for small sets like this. If it was a large set of nodes, you'd want to consider using .reduce(), which could do it in one loop (at the cost of readability).

const nodes = [
  {nodeName: 'node1', nodeId: 1, checked: false },
  {nodeName: 'node2', nodeId: 2, checked: true },
  {nodeName: 'node3', nodeId: 3, checked: false },
  {nodeName: 'node4', nodeId: 4, checked: true },
  {nodeName: 'node5', nodeId: 5, checked: false },
  {nodeName: 'node6', nodeId: 6, checked: true },
]

const checkedNodes = nodes
  .reduce((acc, node) => {
    if (node.checked) {
      acc.push({
        name: node.nodeName,
        id: node.nodeId,
        checked: node.checked
      })
    }

    return acc;
  }, []);

console.log(checkedNodes);

CodePudding user response：

Using Array#map & Array#filter:

const nodes = [ {nodeName: 'node1', nodeId: 1, checked: false }, {nodeName: 'node2', nodeId: 2, checked: true }, {nodeName: 'node3', nodeId: 3, checked: false }, {nodeName: 'node4', nodeId: 4, checked: true }, {nodeName: 'node5', nodeId: 5, checked: false }, {nodeName: 'node6', nodeId: 6, checked: true } ];

const chekedNodes = nodes
  .filter(node => node.checked === true)
  .map(node => ({ name: node.nodeName, id: node.nodeId, checked: node.checked }));

console.log(chekedNodes);

Using Array#reduce:

const nodes = [ {nodeName: 'node1', nodeId: 1, checked: false }, {nodeName: 'node2', nodeId: 2, checked: true }, {nodeName: 'node3', nodeId: 3, checked: false }, {nodeName: 'node4', nodeId: 4, checked: true }, {nodeName: 'node5', nodeId: 5, checked: false }, {nodeName: 'node6', nodeId: 6, checked: true } ];

const chekedNodes = nodes.reduce((list, node) => {
  if(node.checked === true) {
    list.push({ name: node.nodeName, id: node.nodeId, checked: node.checked });
  }
  return list;
}, []);

console.log(chekedNodes);

CodePudding user response：

You should use filter and map to get the desired array;

nodes.filter(n => n.checked)
  .map(n => ({id: n.nodeId,
    name: n.nodeName,
    checked})

CodePudding user response：

You can use filter() method of array.
below we are iterating though the array and returning node object whenever node.checked is true.

let data = [{
    nodeName: 'node1',
    nodeId: 1,
    checked: false
  },
  {
    nodeName: 'node2',
    nodeId: 2,
    checked: true
  },
  {
    nodeName: 'node3',
    nodeId: 3,
    checked: false
  },
  {
    nodeName: 'node4',
    nodeId: 4,
    checked: true
  },
  {
    nodeName: 'node5',
    nodeId: 5,
    checked: false
  },
  {
    nodeName: 'node6',
    nodeId: 6,
    checked: true
  },
]
// we are using filter method of array and just returning node.checked is true.
let result = data.filter(node => {
  if (node.checked) {
    return node;
  }
});
console.log(result);