I have a nested array like shown below.

var arr1 = ['a', 'b', ['c', 'd'], ['e', 'f']];

Is there a way to use another, un-nested array as the key(s) for arr1?

var arr1 = ['a', 'b', ['c', 'd'], ['e', 'f']];
var arr2 = [3, 0];
var arr3 = [4, 1];

console.log(arr1[arr2]); // should return 'c' like arr1[3][0]
console.log(arr1[arr3]); // instead of arr1[4][1]; should return 'f'

Is there a function that allows me to do this?

CodePudding user response：

You can make your own function that implements this behavior like so:

function nested_access(arr1, arr2) {
    let ret = arr1;
    arr2.forEach((index) => {
        ret = ret[index];
    });
    return ret;
}

const arr1 = ['a', 'b', ['c', 'd'], ['e', 'f']];
const arr2 = [2, 0];
const arr3 = [3, 1];

console.log(nested_access(arr1, arr2)); // should return 'c'
console.log(nested_access(arr1, arr3)); // should return 'f'

CodePudding user response：

Just a simple method with reduce to walk the tree. (I changed your example indexes since they were off)

const lookUp = (arr, indexes) =>
  indexes.reduce(
    (acc, index) => acc[index],
    arr);


var arr1 = ['a', 'b', ['c', 'd'],
  ['e', 'f']
];
var arr2 = [2, 0];
var arr3 = [3, 1];

console.log(lookUp(arr1, arr2));
console.log(lookUp(arr1, arr3));

CodePudding user response：

You can find the value by iteratively accessing properties using an array of property accessors:

function findValue (obj, propertyAccessors) {
  try {
    let result = obj;
    for (const key of propertyAccessors) result = result[key];
    return result;
  }
  catch {
    return undefined;
  }
}

const arr1 = ['a', 'b', ['c', 'd'], ['e', 'f']];
const arr2 = [2, 0];
const arr3 = [3, 1];

console.log(findValue(arr1, arr2)); // "c"
console.log(findValue(arr1, arr3)); // "f"
console.log(findValue(arr1, [2, 2, 3])); // undefined

If you attempt to access a property which doesn't exist, the result will be undefined. If you continue to attempt to access another property on undefined, an exception will be thrown. By using try...catch, you can catch such an error and return undefined.

CodePudding user response：

Try this:

function getValue(arr, arrKeys)
{
  return arrKeys.reduce(
    (acum, current) =>  acum?.[current]
    , arr
  )
}

var arr1 = ['a', 'b', ['c', 'd'], ['e', 'f']];
var arr2 = [2, 0];
var arr3 = [3, 1];

console.log(getValue(arr1, arr2))
console.log(getValue(arr1, arr3))

CodePudding user response：

You can create an array method Array#getNested as follows:

Array.prototype.getNested = function(index) { 
    let out = this; 
    index.forEach(i => out = out[i]); 
    return out; 
}

const arr1 = ['a', 'b', ['c', 'd'], ['e', 'f'], ['g',['h',['i', 'j']]]];
const arr2 = [2, 0];
const arr3 = [3, 1];
const arr4 = [4, 1, 1, 0];

console.log( arr1.getNested(arr2) );
console.log( arr1.getNested(arr3) );
console.log( arr1.getNested(arr4) );