Develop Reference

convert array into object name and values

I am trying to place my _rows values into my object value , however i have tried running a loop but i wasnt able to get the data out , the script i used is
let _columns = ["Name", "age", "phone"]
let _rows = [[{ value: 'john' }, { value: '22' }, { value: '999' }], [{ value: 'Bob' }, { value: '21' }, { value: '222' }]]
let res = {}
for (let i = 0; i < _rows.length; i++) {
for (let a = 0; a < _columns.length; a++) {
console.log(_rows[i][a].value)
}
res = _columns.reduce((acc,curr)=> (acc[curr]="data",acc),{});
console.log(res)
res = {}
}
on my console.log , it prints
The target output should be
{Name: 'john', age: '22', phone: '999'}
{Name: 'bob', age: '21', phone: '222'}

you can use
array.map to build another array from _rows
foreach value you have to check if columns exist
if (_columns[index]) {
if yes add in the new object the value under column name
res[_columns[index]] = property.value;
let _columns = ["Name", "age", "phone"]
let _rows = [[{ value: 'john' }, { value: '22' }, { value: '999' }], [{ value: 'Bob' }, { value: '21' }, { value: '222' }]];
let result = _rows.map(one => {
let res = {};
one.forEach((property, index) => {
if (_columns[index]) {
res[_columns[index]] = property.value;
}
});
return res;
});
console.log(result);

If you want to stick with reduce, just make this small change to get the actual value instead of the hardcode string "data". You need to use the optional parameter currentIndex of the reduce callback, then use the index to access the row item for the value.
let _columns = ["Name", "age", "phone"]
let _rows = [[{ value: 'john' }, { value: '22' }, { value: '999' }], [{ value: 'Bob' }, { value: '21' }, { value: '222' }]]
let res = {}
for (let i = 0; i < _rows.length; i++) {
for (let a = 0; a < _columns.length; a++) {
console.log(_rows[i][a].value)
}
res = _columns.reduce((acc,curr,index)=> (acc[curr]=_rows[i][index].value,acc),{});
console.log(res)
res = {}
}
However, when dealing with rows and columns in your case, since the array index is important, using old-school nested for-loop might be much more clear sometimes. My experience is, when you need the array index anyway, try not to be fancy and go for regular for-loop.
let _columns = ["Name", "age", "phone"]
let _rows = [[{ value: 'john' }, { value: '22' }, { value: '999' }], [{ value: 'Bob' }, { value: '21' }, { value: '222' }]]
for(let i = 0; i < _rows.length; i++)
{
let res = {};
for(let j = 0; j < _columns.length; j++)
{
res[_columns[j]] = _rows[i][j].value
}
console.log(res);
}

A double Arry.map will do the trick
let _columns = ["Name", "age", "phone"]
let _rows = [
[{ value: 'john' }, { value: '22' }, { value: '999' }],
[{ value: 'Bob' }, { value: '21' }, { value: '222' }]
];
const output = _rows.map((row) => row.map((item, index) => ({ [_columns[index]]: item.value })));
console.log(output)

How to rearrange array of objects to new array of Objects

I have an array of objects with the same keys, example:
const data = [{name: "firstName", value: "John"},
{name: "lastName", value: "Smith"},
{name: "Number", value: "421-8686"}
]
I however want the values to become the key and values. example:
const data = [{"firstName": "John"},
{"lastName": "Smith"},
{"Number": "421-8686"}]
I tried a few methods, but for some reason or another I fail. My latest attempt is:
let newData = {}
arrayData.forEach((item, index) => {
let key = data.name
let value = data.value
newData[index] = { key: value} // this results in {"key": "John"} --> but i want {"firstName": "John"}
});

You can use Object.fromEntries.
let data = [
{name: "firstName", value: "John"},
{name: "lastName", value: "Smith"},
{name: "Number", value: "421-8686"}
]
data = data.map(info => Object.fromEntries([[info.name, info.value]]))
console.log(data)

const data = [{name: "firstName", value: "John"},
{name: "lastName", value: "Smith"},
{name: "Number", value: "421-8686"}
]
/*const data = [{"firstName": "John"},
{"lastName": "Smith"},
{"Number": "421-8686"}]
*/
for(let i = 0;i < data.length;i++){
data[i][data[i].name] = data[i].value // creates new key value pair
delete data[i].name // deletes old key
delete data[i].value
}
console.log(data)

let data = [
{ name: "firstName", value: "John" },
{ name: "lastName", value: "Smith" },
{ name: "Number", value: "421-8686" },
];
// map the data to required format.
data = data.map((d) => {
let o = {};
o[d["name"]] = d["value"];
return o;
});
console.log("data",data);

I believe you should get result as following, what you want.
Of course, I confirmed status.
const data = [{name: "firstName", value: "John"},
{name: "lastName", value: "Smith"},
{name: "Number", value: "421-8686"}
]
let newData = [];
data.forEach((item) => {
let obj = {};
obj[item.name] = item.value;
newData.push( obj );
});
console.log(newData);
Thanks.

Just a small tweak to your code. Property has to be dynamically created.
In ES6, we can dynamically create a property key by placing the key in square brackets [].
const data = [
{ name: "firstName", value: "John" },
{ name: "lastName", value: "Smith" },
{ name: "Number", value: "421-8686" }
];
let newData = [];
data.forEach((item, index) => newData[index] = {[item.name]: item.value});
console.log(newData)

How to populate an array of objects dynamically?

let products = [
{
name: "a",
inventory: 1
},
{
name: "b",
inventory: 2
},
{
name: "c",
inventory: 3
}
];
How can I go about creating these objects in an array like this dynamically ?
Here is what I have been trying to do.
choicesHolder = [{name: '', inventory: ''}];
for(i; element.length<0; i--) {
choicesHolder.push({"name": element.value, "inventory": element.selected});
}
element holds the data from the JSON.

You can use the map method.
MDN docs about map
const choicesHolder = arrayOfElement.map(element => {
return {
name: element.value,
inventory: element.selected
}
})

Try this:
let res = [];
let char = 'a'
for (let i = 0; i < 4; i++) {
res.push({ "name": char, "inventory": i + 1 });
char = String.fromCharCode(char.charCodeAt(0) + 1) // 'B'
}
console.log(res)

how to write a loop for search array

I want to learn how to make this code cleaner. I am using JavaScript.
Here is an Array of Objects:
var arr = [
{ key: 'qqqqq', value: '11' },
{ key: 'aaaaa', value: '121' },
{ key: 'bbbbb', value: '131' },
{ key: 'ccccc', value: '141' },
]
var obj = { key: 'cccc', value: '-fd-' };
My target is to find if obj in arr(it means, arritem.key == obj.key), if it does, update the value, otherwise append the obj to arr.
The idea of a directly is:
let has = false;
for(const item of arr) {
if(item.key == obj.key) {
item.value = obj.value;
has = true;
break;
}
}
if(!has) {
arr.push(l);
}
It's there a cleaner way to achieve ?

Unless you're restricted to using that given format for the array, you can achieve what you want by turning it into an object or key/value pair...
var data = {
'qqqqq': '11',
'aaaaa': '121',
'bbbbb': '131',
'ccccc': '141'
}
then to add or update a value...
data['ccccc'] = '-fd-'; // updates ccccc
data['eeeee'] = 'new'; // adds eeeee

You could use Array#find for getting the object or if not found push obj to the array.
var arr = [{ key: 'qqqqq', value: '11' }, { key: 'aaaaa', value: '121' }, { key: 'bbbbb', value: '131' }, { key: 'ccccc', value: '141' }],
obj = { key: 'cccc', value: '-fd-' };
temp = arr.find(o => o.key === obj.key);
if (temp) {
temp.value = obj.value;
} else {
arr.push(obj);
}
console.log(arr);
.as-console-wrapper { max-height: 100% !important; top: 0; }

You've to first search if item exist in your array, you can use findIndex => if item is found just replace the value at the finded index by your new object else push it into your array.
var arr = [
{ key: 'qqqqq', value: '11' },
{ key: 'aaaaa', value: '121' },
{ key: 'bbbbb', value: '131' },
{ key: 'ccccc', value: '141' },
]
var obj = { key: 'cccc', value: '-fd-' };
var obj2 = { key: 'aaaaa', value: 'newValue' };
function updateOrPush(arr,obj){
var id = arr.findIndex(e => e.key == obj.key);
if(id > -1){
arr[id] = obj;
}
else{
arr.push(obj);
}
}
updateOrPush(arr,obj);
updateOrPush(arr,obj2);
console.log(arr)

Hope this code would be simpler
var arr = [
{ key: 'qqqqq', value: '11' },
{ key: 'aaaaa', value: '121' },
{ key: 'bbbbb', value: '131' },
{ key: 'ccccc', value: '141' },
]
var obj = { key: 'cccc', value: '-fd-' };
var objIndex = arr.findIndex(ele => ele.key === obj.key);
objIndex < 0 ? arr.push(obj) : arr[objIndex].value = obj.value;
console.log(arr);

Merge JavaScript objects in array with same key

What is the best way to merge array contents from JavaScript objects sharing a key in common?
How can array in the example below be reorganized into output? Here, all value keys (whether an array or not) are merged into all objects sharing the same name key.
var array = [
{
name: "foo1",
value: "val1"
}, {
name: "foo1",
value: [
"val2",
"val3"
]
}, {
name: "foo2",
value: "val4"
}
];
var output = [
{
name: "foo1",
value: [
"val1",
"val2",
"val3"
]
}, {
name: "foo2",
value: [
"val4"
]
}
];

Here is one option:-
var array = [{
name: "foo1",
value: "val1"
}, {
name: "foo1",
value: ["val2", "val3"]
}, {
name: "foo2",
value: "val4"
}];
var output = [];
array.forEach(function(item) {
var existing = output.filter(function(v, i) {
return v.name == item.name;
});
if (existing.length) {
var existingIndex = output.indexOf(existing[0]);
output[existingIndex].value = output[existingIndex].value.concat(item.value);
} else {
if (typeof item.value == 'string')
item.value = [item.value];
output.push(item);
}
});
console.dir(output);

Here is another way of achieving that goal:
var array = [{
name: "foo1",
value: "val1"
}, {
name: "foo1",
value: [
"val2",
"val3"
]
}, {
name: "foo2",
value: "val4"
}];
var output = array.reduce(function(o, cur) {
// Get the index of the key-value pair.
var occurs = o.reduce(function(n, item, i) {
return (item.name === cur.name) ? i : n;
}, -1);
// If the name is found,
if (occurs >= 0) {
// append the current value to its list of values.
o[occurs].value = o[occurs].value.concat(cur.value);
// Otherwise,
} else {
// add the current item to o (but make sure the value is an array).
var obj = {
name: cur.name,
value: [cur.value]
};
o = o.concat([obj]);
}
return o;
}, []);
console.log(output);

2021 version
Using reduce to aggregate data.
Using logical nullish assignment only assigns if acc[name] is nullish (null or undefined).
Using Array.isArray to determines whether the passed value is an Array.
var arrays = [{ name: "foo1",value: "val1" }, {name: "foo1", value: ["val2", "val3"] }, {name: "foo2",value: "val4"}];
const result = arrays.reduce((acc, {name, value}) => {
acc[name] ??= {name: name, value: []};
if(Array.isArray(value)) // if it's array type then concat
acc[name].value = acc[name].value.concat(value);
else
acc[name].value.push(value);
return acc;
}, {});
console.log(Object.values(result));

Using lodash
var array = [{name:"foo1",value:"val1"},{name:"foo1",value:["val2","val3"]},{name:"foo2",value:"val4"}];
function mergeNames (arr) {
return _.chain(arr).groupBy('name').mapValues(function (v) {
return _.chain(v).pluck('value').flattenDeep();
}).value();
}
console.log(mergeNames(array));

Here is a version using an ES6 Map:
const arrays = [{ name: "foo1",value: "val1" }, {name: "foo1", value: ["val2", "val3"] }, {name: "foo2",value: "val4"}];
const map = new Map(arrays.map(({name, value}) => [name, { name, value: [] }]));
for (let {name, value} of arrays) map.get(name).value.push(...[value].flat());
console.log([...map.values()]);

Use lodash "uniqWith". As shown below
let _ = require("lodash");
var array = [
{ name: "foo1", value: "1" },
{ name: "foo1", value: "2" },
{ name: "foo2", value: "3" },
{ name: "foo1", value: "4" }
];
let merged = _.uniqWith(array, (pre, cur) => {
if (pre.name == cur.name) {
cur.value = cur.value + "," + pre.value;
return true;
}
return false;
});
console.log(merged);
// output: [{ name: "foo1", value: "1,2,4" }, { name: "foo2", value: "3" }];

Using reduce:
var mergedObj = array.reduce((acc, obj) => {
if (acc[obj.name]) {
acc[obj.name].value = acc[obj.name].value.isArray ?
acc[obj.name].value.concat(obj.value) :
[acc[obj.name].value].concat(obj.value);
} else {
acc[obj.name] = obj;
}
return acc;
}, {});
let output = [];
for (let prop in mergedObj) {
output.push(mergedObj[prop])
}

It's been a while since this question was asked, but I thought I'd chime in as well. For functions like this that execute a basic function you'll want to use over and over, I prefer to avoid longer-written functions and loops if I can help it and develop the function as a one-liner using shallow Array.prototype functions like .map() and some other ES6+ goodies like Object.entries() and Object.fromEntries(). Combining all these, we can execute a function like this relatively easily.
First, I take in however many objects you pass to the function as a rest parameter and prepend that with an empty object we'll use to collect all the keys and values.
[{}, ...objs]
Next, I use the .map() Array prototype function paired with Object.entries() to loop through all the entries of each object, and any sub-array elements each contains and then either set the empty object's key to that value if it has not yet been declared, or I push the new values to the object key if it has been declared.
[{},...objs].map((e,i,a) => i ? Object.entries(e).map(f => (a[0][f[0]] ? a[0][f[0]].push(...([f[1]].flat())) : (a[0][f[0]] = [f[1]].flat()))) : e)[0]
Finally, to replace any single-element-arrays with their contained value, I run another .map() function on the result array using both Object.entries() and Object.fromEntries(), similar to how we did before.
let getMergedObjs = (...objs) => Object.fromEntries(Object.entries([{},...objs].map((e,i,a) => i ? Object.entries(e).map(f => (a[0][f[0]] ? a[0][f[0]].push(...([f[1]].flat())) : (a[0][f[0]] = [f[1]].flat()))) : e)[0]).map(e => e.map((f,i) => i ? (f.length > 1 ? f : f[0]) : f)));
This will leave you with the final merged object, exactly as you prescribed it.
let a = {
a: [1,9],
b: 1,
c: 1
}
let b = {
a: 2,
b: 2
}
let c = {
b: 3,
c: 3,
d: 5
}
let getMergedObjs = (...objs) => Object.fromEntries(Object.entries([{},...objs].map((e,i,a) => i ? Object.entries(e).map(f => (a[0][f[0]] ? a[0][f[0]].push(...([f[1]].flat())) : (a[0][f[0]] = [f[1]].flat()))) : e)[0]).map(e => e.map((f,i) => i ? (f.length > 1 ? f : f[0]) : f)));
getMergedObjs(a,b,c); // { a: [ 1, 9, 2 ], b: [ 1, 2, 3 ], c: [ 1, 3 ], d: 5 }

Try this:
var array = [{name:"foo1",value:"val1"},{name:"foo1",value:["val2","val3"]},{name:"foo2",value:"val4"},{name:"foo2",value:"val5"}];
for(var j=0;j<array.length;j++){
var current = array[j];
for(var i=j+1;i<array.length;i++){
if(current.name = array[i].name){
if(!isArray(current.value))
current.value = [ current.value ];
if(isArray(array[i].value))
for(var v=0;v<array[i].value.length;v++)
current.value.push(array[i].value[v]);
else
current.value.push(array[i].value);
array.splice(i,1);
i++;
}
}
}
function isArray(myArray) {
return myArray.constructor.toString().indexOf("Array") > -1;
}
document.write(JSON.stringify(array));

This work too !
var array = [
{
name: "foo1",
value: "val1",
},
{
name: "foo1",
value: ["val2", "val3"],
},
{
name: "foo2",
value: "val4",
},
];
let arr2 = [];
array.forEach((element) => { // remove duplicate name
let match = arr2.find((r) => r.name == element.name);
if (match) {
} else {
arr2.push({ name: element.name, value: [] });
}
});
arr2.map((item) => {
array.map((e) => {
if (e.name == item.name) {
if (typeof e.value == "object") { //lets map if value is an object
e.value.map((z) => {
item.value.push(z);
});
} else {
item.value.push(e.value);
}
}
});
});
console.log(arr2);

const exampleObj = [{
year: 2016,
abd: 123
}, {
year: 2016,
abdc: 123
}, {
year: 2017,
abdcxc: 123
}, {
year: 2017,
abdcxcx: 123
}];
const listOfYears = [];
const finalObj = [];
exampleObj.map(sample => {    
listOfYears.push(sample.year);
});
const uniqueList = [...new Set(listOfYears)];
uniqueList.map(list => {   
finalObj.push({
year: list
});
});
exampleObj.map(sample => {    
const sampleYear = sample.year;  
finalObj.map((obj, index) => {     
if (obj.year === sampleYear) {        
finalObj[index] = Object.assign(sample, obj);       
}  
}); 
});
The final object be [{"year":2016,"abdc":123,"abd":123},{"year":2017,"abdcxcx":123,"abdcxc":123}]

const array = [{ name: "foo1", value: "val1" }, {name: "foo1", value: ["val2", "val3"] }, {name: "foo2", value: "val4"}];
const start = array.reduce((object, {name}) => ({...object, [name]: []}), {});
const result = array.reduce((object, {name, value}) => ({...object, [name]: [object[name], [value]].flat(2)}), start);
const output = Object.entries(result).map(([name, value]) => ({name: name, value: value}));
console.log(output);

try this :
var array = [
{
name: "foo1",
value: "val1"
}, {
name: "foo1",
value: [
"val2",
"val3"
]
}, {
name: "foo2",
value: "val4"
}
];
var output = [
{
name: "foo1",
value: [
"val1",
"val2",
"val3"
]
}, {
name: "foo2",
value: [
"val4"
]
}
];
bb = Object.assign( {}, array, output );
console.log(bb) ;

A much more easier approach is this 2022:
var array = [
{
name: "foo1",
value: "val1"
}, {
name: "foo1",
value: [
"val2",
"val3"
]
}, {
name: "foo2",
value: "val4"
}
];
var output = [
{
name: "foo1",
value: [
"val1",
"val2",
"val3"
]
},
{
name: "foo2",
value: [
"val4"
]
}
];
function mergeBasedOnKey(list){
let c = Object.values(list.reduce((a, b) => {
a[b.name] = a[b.name] || {name: b.name, value: []}
if(typeof(b['value']) == "string"){
a[b.name].value.push(b['value'])
}
else{
a[b.name].value = [...a[b.name].value, ...b.value]
}
return a
}, {}))
return c
}
let ans = mergeBasedOnKey(array)
console.log(ans)

I was looking for a quick, almost "one-liner" answer in this thread, provided that this is a trivial but common exercise.
I couldn't find any for my like. The other answers are fine but I am not much into boilerplate.
So, let me add one, then:
o = array.reduce((m,{name:n,value:v})=>({...m,[n]:[...m[n]||[],v].flat(1)}),{})
output = Object.entries(o).map(([n,v])=>({name:n,value:v}))
var array = [
{ name: "foo1", value: "val1"},
{ name: "foo1", value: ["val2","val3"] },
{ name: "foo2", value: "val4" }
]
o=array.reduce((m,{name:n,value:v})=>({...m,[n]:[...m[n]||[],v].flat(1)}),{})
output=Object.entries(o).map(([n,v])=>({name:n,value:v}))
console.log(output)