Develop Reference

Transforming array of objects based upon key - javascript

I am trying to figure out the most efficient method for reducing an array of objects based upon a unique key (key/values are dynamically returned in this case). I've tried to a combination of different methods using concat, map, or filter but haven't had much luck.
Original array of objects:
[
{
key: "Name",
value: "John"
},
{
key: "Company",
value: "Acme"
},
{
key: "Name",
value: "Jack"
},
{
key: "Name",
value: "Matt"
},
{
key: "Last",
value: "Test"
}
]
Desired Array:
[
{
key: "Name",
values: [
"John",
"Jack",
"Matt"
]
},
{
key: "Company",
values: [
"Acme"
]
},
{
key: "Last",
values: [
"Test"
]
}
]

Prob other ways, but a simple for loop would suffice:
const data = [{
key: "Name",
value: "John"
},
{
key: "Company",
value: "Acme"
},
{
key: "Name",
value: "Jack"
},
{
key: "Name",
value: "Matt"
},
{
key: "Last",
value: "Test"
}
]
let result = {}
for (const i in data) {
result[data[i].key] = {
key: data[i].key,
values: [
...result[data[i].key] ? result[data[i].key].values : [],
data[i].value
]
}
}
console.log(Object.values(result))

You can use reduce to build a new object using name as the keys, and then use Object.values to create the output you need from the object:
const data = [
{ key: "Name", value: "John" },
{ key: "Company", value: "Acme" },
{ key: "Name", value: "Jack" },
{ key: "Name", value: "Matt" },
{ key: "Last", value: "Test" }
];
const out = Object.values(data.reduce((acc, { key, value }) => {
// If the key doesn't exist on the object, add it
// and initialise the value object
acc[key] = acc[key] || { key, values: [] };
// Push the value from the current iteration
// into the values array
acc[key].values.push(value);
// Return the accumulator for the next iteration
return acc;
}, {}));
console.log(out);

I think reduce is the best solution here :)
const initialArray = [
{
key: "Name",
value: "John"
},
{
key: "Company",
value: "Acme"
},
{
key: "Name",
value: "Jack"
},
{
key: "Name",
value: "Matt"
},
{
key: "Last",
value: "Test"
}
];
const result = initialArray.reduce((acc, obj) => {
/* try to find object in the result array
returns index or -1 if object is missing
*/
const existingIndex = acc.findIndex(item => item.key === obj.key);
if (existingIndex > -1) {
/* object already exists, update its values array */
acc[existingIndex].values.push(obj.value);
return acc;
} else {
/* the key is first encountered, create an object in the result array */
acc.push({
key: obj.key,
values: [obj.value],
});
return acc;
}
}, []); // [] - default value is an empty array
console.log(result);

javascript array tree search keep the node and parents

Trying to implement a tree search function which takes an array(tree structure) and a string keyword, would return an tree array but only keep the matched nodes and its parents.
function search(nodes, keyword){
}
const nodes = [
{
value: "1-1",
children: [
{ value: "1-1-1"},
{ value: "1-1-2", children:[
{
value: "1-1-2-1",
children: [
{ value: "1-1-2-1-1" },
{ value: "1-1-2-1-2" }
]
},
{
value: "1-1-2-2"
}
] }
]
},
{
value: "1-2",
children: [
{ value: "1-2-1"},
{ value: "1-2-2", children:[
{
value: "1-2-2-1",
children: [
{ value: "1-2-2-1-1" },
{ value: "1-2-2-1-2" }
]
},
{
value: "1-2-2-2"
}
] }
]
},
];
expected output would be an tree with nodes' values contain "1-1-2-1" and its parents as below
const searchedNodes = search(nodes, "1-1-2-1");
[
{
value: "1-1",
children: [
{ value: "1-1-2", children:[
{
value: "1-1-2-1",
children: [
{ value: "1-1-2-1-1" }
]
}
] }
]
}
]
*/
2018-06-26 Updated
I made a working one(DFS) but probably not pretty efficient.
const search = (nodes, keyword) => {
let newNodes = [];
for (let n of nodes) {
if (n.children) {
const nextNodes = this.keywordFilter(n.children, keyword);
if (nextNodes.length > 0) {
n.children = nextNodes;
} else if (n.label.toLowerCase().includes(keyword.toLowerCase())) {
n.children = nextNodes.length > 0 ? nextNodes : [];
}
if (
nextNodes.length > 0 ||
n.label.toLowerCase().includes(keyword.toLowerCase())
) {
newNodes.push(n);
}
} else {
if (n.label.toLowerCase().includes(keyword.toLowerCase())) {
newNodes.push(n);
}
}
}
return newNodes;
};

You need to iterate the nodes of the same level and check if the value is equal, then take that node and exit the loop. Otherwise check the children and generate a new object for preventing to mutate the original data.
function search(nodes, value) {
var result;
nodes.some(o => {
var children;
if (o.value === value) {
return result = o;
}
if (o.children && (children = search(o.children, value))) {
return result = Object.assign({}, o, { children });
}
});
return result && [result];
}
const nodes = [{ value: "1-1", children: [{ value: "1-1-1" }, { value: "1-1-2", children: [{ value: "1-1-2-1", children: [{ value: "1-1-2-1-1" }, { value: "1-1-2-1-2" }] }, { value: "1-1-2-2" }] }] }, { value: "1-2", children: [{ value: "1-2-1" }, { value: "1-2-2", children: [{ value: "1-2-2-1", children: [{ value: "1-2-2-1-1" }, { value: "1-2-2-1-2" }] }, { value: "1-2-2-2" }] }] }];
console.log(search(nodes, "1-1-2-1"));
.as-console-wrapper { max-height: 100% !important; top: 0; }

Convert json to other json structure

I have an array of objects with this structure:
const treeData = [
{ 0: ["0-0", "0-1"] },
{ 1: ["1-0", "1-1"] }
]
It could be deeper but array data would be always json or strings
const treeData = [
{ 0: ["0-0", "0-1"] },
{ 1: ["1-0", "1-1"] },
2,
3
]
I would like to get something like this:
const treeDataResult = [
{
label: "0",
value: "0",
children: [
{
label: "0-0",
value: "0-0"
},
{
label: "0-1",
value: "0-1",
}
]
},
{
label: "1",
value: "1",
children: [
{
label: "1-0",
value: "1-0",
},
{
label: "1-1",
value: "1-1",
}
]
},
{
label: "2",
value: "2"
},
{
label: "3",
value: "3"
}
]
My code right now is this:
const treeData = [
{ "0": ["0-0", "0-1"] },
{ "1" : ["1-0", "1-1"] }
];
const convertNode = (parentNode) =>
parentNode.map(
childnode => {
if (typeof(childNode) === 'string')
return {
label: childNode,
value: childNode
}
else
return
childNode.map((key, val) =>
({
label: key,
value: key,
children: convertNode(val)
})
)
}
)
var treeDataResult = convertNode(treeData);
console.log(treeDataResult);

If JSON.parse is used to get the data, you can try something like this:
var j = '[ { "0": ["0-0", "0-1"] }, { "1": ["1-0", "1-1"] }, 2, 3 ]'
var o = JSON.parse(j, (k, v) => (k = v.constructor) === Array ? v :
k !== Object ? ({ label: v, value: v }) :
({ label: k = Object.keys(v)[0], value: k, children: v[k] }) )
console.log( o )

If the shape of your data is correct I've used reduce and map to get the data into the correct shape and the rest operator so that the objects are in one array
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/reduce
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Spread_syntax
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/keys
const treeData = [
{
0: ["0-0", "0-1"]
},
{
1: ["1-0", "1-1"]
},
{
2: null
},
{
3: []
},
{
4: ["0-1"]
}
]
const changeShape = data => {
return data.reduce((prev, curr) => [...prev, ...shape(curr)], []);
}
const shape = item => Object.keys(item).map(key => data(item, key));
const data = (item, key) => {
return !item[key] || !item[key].length > 0 ?
labelValue(key) :
{
...labelValue(key),
children: item[key].map(i => labelValue(i))
}
}
const labelValue = v => {
return {
label: v,
value: v
}
}
console.log(changeShape(treeData))

const treeData = [
{ "0": ["0-0", "0-1"] },
{ "1" : ["1-0", "1-1"] }
];
const convertNode = (parentNode) => {
console.log(parentNode)
return parentNode.map(
childNode => {
if (typeof childNode === 'string')
return {
label: childNode,
value: childNode
}
else
return {
label: Object.entries(childNode)[0][0],
value: Object.entries(childNode)[0][0],
children: convertNode(Object.entries(childNode)[0][1])
}
}
)
}

a primitive solution
const treeData = [
{ 0 : ["0-0", "0-1"] },
{ 1 : ["1-0", "1-1"] }
]
let treeDataResult = [];
for(i = 0; i < treeData.length; i++) {
let current = treeData[i],
label = Object.getOwnPropertyNames(current),
obj = {
label: label,
value: label,
children: []
}
for(j = 0; j < current[i].length; j++) {
let childData = current[i][j],
child = {
label : childData,
value : childData
}
obj.children.push(child)
}
treeDataResult.push(obj)
}
console.log(JSON.stringify(treeDataResult, null, 4));

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)