Create new array using elements of one array as an index to select elements in a different array - JavaScript

Question

It took almost a day and half to accomplish this, and I still am not sure why it works. If there's a better way(s) to accomplish, I'd love to hear it. In its present state, I hope this helps someone.

var newValuesArray = [];
var arrayIndex = [1, 4, 9];
var valuesArray = [["Zero", "One", "Two", "Three", "Four", "Five", "Six", "Seven", "Eight", "Nine"], 
              ["A", "B", "C", "D", "E", "F", "G", "H", "I", "J"]
              ];

var roots = valuesArray.map(function(num) {
    arrayIndex[num];
    return arrayIndex;
});

for (var i = 0, len = roots.length; i < len; i++) {
  newValuesArray.push(roots[i].map(function(num) {
     return valuesArray[i][num];
  }));
}

console.log(newValuesArray);

This is the result I was looking for which the code above produces:

[["One", "Four", "Nine"], ["B", "E", "J"]]

Will arrayIndex always be in ascending order? What is the expected result if arrayIndex = [4, 9, 1];? — Paul Roub
– Paul Roub, Commented Oct 15, 2015 at 16:56

Pranav C Balan · Accepted Answer · 2015-10-15 17:13:35Z

6

You can use map() and filter()

var arrayIndex = [1, 4, 9];
var valuesArray = [
  ["Zero", "One", "Two", "Three", "Four", "Five", "Six", "Seven", "Eight", "Nine"],
  ["A", "B", "C", "D", "E", "F", "G", "H", "I", "J"]
];

// iterate over main array using map()
var newValuesArray = valuesArray.map(function(v) {
  // iterate and filter values in inner array using filfer()
  return v.filter(function(v1, i) {
    // check index in arrayIndex
    return arrayIndex.indexOf(i) > -1;
  });
});

document.write('<pre>'+JSON.stringify(newValuesArray,null,3)+'</pre>');

Update: In case , if you need to get values in same order of index array then use

var arrayIndex = [4, 9, 1];
var valuesArray = [
  ["Zero", "One", "Two", "Three", "Four", "Five", "Six", "Seven", "Eight", "Nine"],
  ["A", "B", "C", "D", "E", "F", "G", "H", "I", "J"]
];

// iterate over main array using map()
var newValuesArray = valuesArray.map(function(v) {
  // iterate the index array
  return arrayIndex.map(function(v1) {
    // get value from inner array based on index
    return v[v1];
  });
});

document.write('<pre>'+JSON.stringify(newValuesArray,null,2)+'</pre>');

edited Oct 15, 2015 at 17:13

answered Oct 15, 2015 at 16:48

Pranav C Balan

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1 Comment

Quint Rahaman Over a year ago

Thanks, @pranav-c-balan!

Nina Scholz · Accepted Answer · 2015-10-15 17:01:46Z

0

You may consider an array method Array.prototype.map for iterating over the valuesArray and for the arrayIndex.

var arrayIndex = [1, 4, 9],
    valuesArray = [
        ["Zero", "One", "Two", "Three", "Four", "Five", "Six", "Seven", "Eight", "Nine"],
        ["A", "B", "C", "D", "E", "F", "G", "H", "I", "J"]
    ],
    newValuesArray = valuesArray.map(function (a) {
        return arrayIndex.map(function (b) {
            return a[b];
        });
    });
document.write('<pre>' + JSON.stringify(newValuesArray, 0, 4) + '</pre>');

edited Oct 15, 2015 at 17:01

answered Oct 15, 2015 at 16:54

Nina Scholz

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Comments

Anonymous0day · Accepted Answer · 2015-10-15 17:17:10Z

One solution :

var valuesArray = [
  ["Zero", "One", "Two", "Three", "Four", "Five", "Six", "Seven", "Eight", "Nine"], 
  ["A", "B", "C", "D", "E", "F", "G", "H", "I", "J"],
  ["blue" , "green" , "yellow" , "orange" , "black" , "white" , "violet" , "pink" , "purple" , "grey" ]
];

/* the function ---------------------------------------------*/
var fn = function(indexed){
  
  return indexed.reduce(function( trans , value){
  
     trans.arr.forEach(function(curArray , i){
        var curBranch = (trans.rep[i] = trans.rep[i] || []);
        curBranch.push( curArray[value]  )
     })
     return trans;
  } , {arr : valuesArray , rep : []}).rep;
 
};


/* the samples -----------------------------------------------*/

var arrayIndex = [1, 4, 9];   
document.write( JSON.stringify( fn(arrayIndex) ) );


arrayIndex = [9, 4, 1];
document.write('<br>' + JSON.stringify( fn(arrayIndex) ) );


arrayIndex = [9, 9, 3, 4, 1];
document.write('<br>' + JSON.stringify( fn(arrayIndex) ) );


arrayIndex = [99, 1, 2];
document.write('<br>' + JSON.stringify( fn(arrayIndex) ) );

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