creating custom array from existing array in javascript

Question

I have an array like below:

var search = [
 { code: "t1", name1: "n1", name2: "n2" },
 { code: "t1", name1: "n5", name2: "n6" },
 { code: "t2", name1: "n10", name2: "n11" },
 { code: "t2", name1: "n18", name2: "n20" },
 { code: "t3", name1: "n18", name2: "n20" },
];

I want to transform this array to the format below:

var finald = [
 { code: "t1", name1: "n1,n5", name2: "n2,n6" },
 { code: "t2", name1: "n10,n18", name2: "11,n20" },
 { code: "t3", name1: "n18", name2: "n20" },
];

I have tried this as below code. but no success. First I gathered all unique codes from the array:

var flags = [];
var codes = [];
for(var z=0; z<search.length; z++){
 if( flags[data[z].code]) continue;
 flags[data[z].code] = true;
 codes.push(data[z].code);
}
var finald = [];
for(var i=0; i<search.length; i++){
 var name1 = [];
 var name2 = [];
 for(var y=0; y<codes.length; y++){
 if(codes[y] == search[i].code ){
 var row = {
 code: codes[y],
 name1:search[i].name1,
 name2:search[i].name2,
 };
 finald.push(row);
 }
 } 
}

Please Help.

• mplungjan: Your array does not look like valid JS
• Exception_al: What is the result that you are getting ? Are you getting anything at all ? What Debug attempts have you made so far ?

Answer 1

it's not exactly what you asked for, but still try this approach.

you basically want to do a 'join' action on the array by the key 'code', so maybe try to convert your array to a map object - key: code , value : {name1, name2}

jsfiddle

var search = [
 {code:"t1", name1:"n1", name2:"n2"},
 {code:"t1", name1:"n5", name2:"n6"},
 {code:"t2", name1:"n10", name2:"n11"},
 {code:"t2", name1:"n18", name2:"n20"},
 {code:"t3", name1:"n18", name2:"n20"}];
const myMap = new Map();
search.forEach((obj) => {
 const key = obj.code;
 if(!myMap.has(key)) {
 myMap.set(key, {
 'name1' : obj.name1,
 'name2' : obj.name2
 });
 } else {
 var ele = myMap.get(key);
 ele.name1 = `${ele.name1},${obj.name1}`;
 ele.name2 = `${ele.name2},${obj.name2}`;
 }
}); 
console.log(myMap);
/*
 key: "t1" => value: {name1:"n1,n5", name2:"n2,n6"},
 key: "t2" => value: {name1:"n10,n18", name2:"n11,n20"},
 key: "t3" => value: {name1:"n18", name2:"n20"}
*/

if you must have it in an array form add this to the above, jsfiddle

var resArray = [];
myMap.forEach((value, key) => {
 resArray.push(Object.assign({'code': key}, value));
});
console.log(resArray);
/*
 [{ code: "t1", name1: "n1,n5", name2: "n2,n6" },
 { code: "t2", name1: "n10,n18", name2: "11,n20" },
 { code: "t3", name1: "n18", name2: "n20" }]
*/

Answer 2

This should do what you want:

var search = [
 { code: "t1", name1: "n1", name2: "n2" },
 { code: "t1", name1: "n5", name2: "n6" },
 { code: "t2", name1: "n10", name2: "n11" },
 { code: "t2", name1: "n18", name2: "n20" },
 { code: "t3", name1: "n18", name2: "n20" }
];
 
const items = search.reduce((acc, item) => {
 const code = item.code;
 if (!acc[code]) acc[code] = {name1: [], name2: []};
 acc[code].name1.push(item.name1);
 acc[code].name2.push(item.name2);
 return acc;
}, {});
const finald = Object.keys(items).reduce((acc, key) => {
 const item = items[key];
 acc.push({
 code: key,
 name1: item.name1.join(','),
 name2: item.name2.join(',')
 });
 return acc;
}, []);

• mplungjan: I think this is much harder to grasp than my version
• Maxime Lequain: You version doesnt take into account the fact that the items in the search array might not be ordered by code
• mplungjan: That is a simple sort. I have assumed it is

Answer 3

I wrote this function:

function normalize(arr) {
 var output = [];
 for(var i = 0; i < arr.length; i++) {
 var codeIndex = _findIndex(output, arr[i].code);
 if(codeIndex !== -1) {
 // Code already in output array, merge names.
 output[_findIndex(output, arr[i].code)].name1 += ', ' + arr[i].name1;
 output[_findIndex(arr[i].code)].name2 += ', ' + arr[i].name2;
 }
 else {
 // Code new to output array, pus into.
 output.push(arr[i]);
 }
 }
 return output;
 //
 // Privates
 //
 function _findIndex(arr, code){
 var index = -1;
 for(var i = 0; i < arr.length; i++){
 if(arr[i].code == code) {
 index = i;
 break;
 }
 }
 return index;
 }
 }

Output:

0 : {code: "t1", name1: "n1, n5", name2: "n2, n6, n20"}
1 : {code: "t2", name1: "n10, n18", name2: "n11"}
2 : {code: "t3", name1: "n18", name2: "n20"}

Answer 4

Something like this?

You could use reduce or map but this is more understandable in my opinion for a simple task

I am assuming the search is ordered by code.

var search = [
 {code:"t1", name1:"n1", name2:"n2"},
 {code:"t1", name1:"n5", name2:"n6"},
 {code:"t2", name1:"n10", name2:"n11"},
 {code:"t2", name1:"n18", name2:"n20"},
 {code:"t3", name1:"n18", name2:"n20"}
 ],
 finald = [];
finald.push(search[0]);
for (var i = 1; i < search.length; i++) {
 var f = finald[finald.length - 1];
 if (f.code == search[i].code) {
 f.name1 += ","+search[i].name1;
 f.name2 += ","+search[i].name2;
 } else {
 finald.push(search[i]);
 }
}
console.log(finald);

Answer 5

You can create your own custom logic for this:

var search = [
 { code: "t1", name1: "n1", name2: "n2" },
 { code: "t1", name1: "n5", name2: "n6" },
 { code: "t2", name1: "n10", name2: "n11" },
 { code: "t2", name1: "n18", name2: "n20" },
 { code: "t3", name1: "n18", name2: "n20" },
];
//this is the result array
var result = [];
//this is a flag
var itemExist = false;
search.forEach((item) => {
 //reset flag to false
 itemExist = false;
 //check if the object already exist in the result array or not
 for(var i=0; i<result.length; i++){
 //if the object exist then merge the values of name1 and name2
 if(result[i].code === item.code){
 result[i].name1 = result[i].name1 +','+item.name1;
 result[i].name2 = result[i].name2 +','+item.name2;
 itemExist = true;
 //break the for loop
 break;
 }
 }
 //if object do not exist in the result array then push it
 if(!itemExist){
 result.push(item);
 }
});
console.log(result);

Answer 6

You can use reduce and map

let search = [{code:"t1", name1:"n1", name2:"n2"},{code:"t1", name1:"n5", name2:"n6"},{code:"t2", name1:"n10", name2:"n11"},{code:"t2", name1:"n18", name2:"n20"},{code:"t3", name1:"n18", name2:"n20"},];
let result = Object.values( search.reduce( (c,v) => {
 c[ v.code ] ? c[ v.code ].push( v ) : c[ v.code ] =[ v ];
 return c;
},{}) ).map( v => {
 let n1 = [], n2 = [];
 v.forEach( e => { n1.push( e.name1 ); n2.push( e.name2 ); });
 return { code : v[0].code, name1 : n1.join(","), name2 : n2.join(",") }
});
console.log( result );

Answer 7

The order of codes doesn't matter here:

const search = [{code:"t1", name1:"n1", name2:"n2"},
 {code:"t1", name1:"n5", name2:"n6"},
 {code:"t2", name1:"n10", name2:"n11"},
 {code:"t2", name1:"n18", name2:"n20"},
 {code:"t3", name1:"n18", name2:"n20"}];
function combineObjectsByCode(objects) {
 let codes = new Set();
 objects.forEach(object => codes.add(object.code));
 let combinedObjects = [];
 codes.forEach(code => {
 let objectsWithSameCode = objects.filter(object => object.code === code);
 let combinedObject;
 objectsWithSameCode.forEach( obj => {
 if (!combinedObject) {
 combinedObject = obj;
 }
 else {
 combinedObject.name1 = combinedObject.name1 + ', ' + obj.name1; 
 combinedObject.name2 = combinedObject.name2 + ', ' + obj.name2; 
 } 
 })
 combinedObjects.push(combinedObject);
 });
 
 return combinedObjects;
}
console.log(combineObjectsByCode(search));

Answer 8

Another take to fix the problem - this code emphasizes on immutability of data, returning new objects from all iterations. This might prevent hard to find bugs when performing such operations:

var finald = transform([
 { code: "t1", name1: "n1", name2: "n2" },
 { code: "t1", name1: "n5", name2: "n6" },
 { code: "t2", name1: "n10", name2: "n11" },
 { code: "t2", name1: "n18", name2: "n20" },
 { code: "t3", name1: "n18", name2: "n20" },
]);
console.log(finald);
function transform(source) {
 const keyedByCode = source.reduce((acc, item) => {
 const { name1 = [], name2 = [] } = acc[item.code] || {};
 return Object.assign({}, acc, {
 [item.code]: {
 name1: [item.name1, ...name1],
 name2: [item.name2, ...name2],
 },
 });
 }, {});
 return Object.keys(keyedByCode).map((code) => ({
 code,
 name1: keyedByCode[code].name1.sort().join(','),
 name2: keyedByCode[code].name2.sort().join(','),
 }));
}

.as-console-wrapper { max-height: 100% !important; }

Answer 9

You can use array#reduce to group your array based on code and push same values in an array. Get all the values using Object.values() and then using array#map convert the array into a string using array#join().

var search = [{ code: "t1", name1: "n1", name2: "n2" },{ code: "t1", name1: "n5", name2: "n6" },{ code: "t2", name1: "n10", name2: "n11" },{ code: "t2", name1: "n18", name2: "n20" },{ code: "t3", name1: "n18", name2: "n20" }],
 result = Object.values(search.reduce((r,{code,name1, name2}) => {
 r[code] = r[code] || {code, name1: [], name2: []};
 r[code].name1.push(name1);
 r[code].name2.push(name2);
 return r;
 },{}))
 .map(({code,name1,name2}) => ({code, name1: name1.join(','), name2: name2.join(',')}));
console.log(result);