Develop Reference

Reduce JSON array to object with combined key-values

I have an array like this:
[
{ "avl_res": 1, "res_status": "Available", "code": "AAA" },
{ "avl_res": 2, "res_status": "Unavailable", "code": "AAA" },
{ "avl_res": 2, "res_status": "Available", "code": "BBB" },
{ "avl_res": 1, "res_status": "Available", "code": "CCC" },
{ "avl_res": 5, "res_status": "Unavailable", "code": "CCC" },
{ "avl_res": 3, "res_status": "Unavailable", "code": "DDD" },
];
I am trying to produce this:
[
{"avl_res":1,"total_res":3,"code":"AAA"},
{"avl_res":2,"total_res":2,"code":"BBB"},
{"avl_res":1,"total_res":6,"code":"CCC"},
{"avl_res":0,"total_res":3,"code":"DDD"},
];
Following the answer to this question, I managed to do it with this:
var singles = {};
arr.forEach(function (item) {
var single = singles[item.code] = singles[item.code] || {};
single[item.res_status] = item.avl_res;
});
var outputList = [];
for (var single in singles) {
let total_res = 0;
let avl_res = 0;
singles[single]['Available'] ? avl_res = singles[single]['Available'] : avl_res = 0;
singles[single]['Unavailable'] ? total_res = avl_res + singles[single]['Unavailable'] : total_res = avl_res;
outputList.push({ code: single, total_res: total_res, avl_res: avl_res });
}
console.log(outputList);
Just wondering if this is efficient enough or there's a better/elegant way, maybe by using other JS functions (e.g. reduce, map, etc.). Cheers!

If you care code performance (efficiency) that much, You would like this...
const arr = [
{ "avl_res": 1, "res_status": "Available", "code": "AAA" },
{ "avl_res": 2, "res_status": "Unavailable", "code": "AAA" },
{ "avl_res": 2, "res_status": "Available", "code": "BBB" },
{ "avl_res": 1, "res_status": "Available", "code": "CCC" },
{ "avl_res": 5, "res_status": "Unavailable", "code": "CCC" },
{ "avl_res": 3, "res_status": "Unavailable", "code": "DDD" },
];
const results = [];
const findItem = {};
for (const { avl_res, code, res_status } of arr) {
let item = findItem[code];
const res = res_status == 'Available' ? avl_res : 0;
if (item) {
item.total_res += avl_res;
item.avl_res += res;
}
else {
item = { avl_res: res, total_res: avl_res, code };
results.push(item);
findItem[code] = item;
}
}
console.log(results);

copying data from one array to another array

Array One:
array1 = [{
"id": 1,
"name": "aaaaa",
"attr": [{"attr_code": "a_id", "value": "5"}]
},
{
"id": 2,
"name": "bbbbb",
"attr": [{"attr": "a_id", "value": "4"}]
}]
Array Two:
array2 = [{
"id": 4,
"name": "bef",
},
{
"id": 5,
"name": "bcd",
}]
Resulting Array:
resultingArray = [{
"id": 1,
"name": "aaaaa",
"attr": [{"attr_code": "a_id", "value": "5"}],
"a_id" : {"id": 5, "name": "bcd"}
},
{
"id": 2,
"name": "bbbbb",
"attr": [{"attr": "a_id", "value": "4"}],
"a_id" : {"id": 4, "name": "bef"}
}]
I am looking to add the array2 objects into array1 based on id's of array2. I have tried using map function on both the arrays to compare and add the object but I didn't succeed. Can you please suggest me how to do it?
Thank you

Add the array2 objects into array1 based on ids of array2.
let array1 =
[
{
"id": 1,
"name": "aaaaa",
"attr": [{"attr_code": "a_id", "value": "5"}]
},
{
"id": 2,
"name": "bbbbb",
"attr": [{"attr": "a_id", "value": "4"}]
}
];
let array2 = [{
"id": 4,
"name": "bef",
},
{
"id": 5,
"name": "bcd",
}
];
let resultingArray=[];
array1.forEach(function(element) {
element['a_id'] = [];
element['attr'].forEach(function(attr) {
element['a_id'].push(array2.find(function(item) {
return item.id == attr.value;
}));
});
resultingArray.push(element)
});
console.log(resultingArray);

I presume you intend to extract the object whose ID is equal to the value field the in the each object in array1.
var array1 = [{
"id": 1,
"name": "aaaaa",
"attr": [{"attr_code": "a_id", "value": "5"}]
},
{
"id": 2,
"name": "bbbbb",
"attr": [{"attr": "a_id", "value": "4"}]
}];
var array2 = [{
"id": 4,
"name": "bef",
},
{
"id": 5,
"name": "bcd",
}];
var resultingArray = [];
for(var i = 0; i < array1.length; i++) {
resultingArray[i] = array1[i];
for(var j = 0; j < array2.length; j++) {
if(resultingArray[i].attr[0].attr_code.value === array2[j].id) {
resultingArray[i].push("a_id": array2[j]);
}
}
}
You just need to lop through array1, and for each object in array1, you need to find corresponding objects in array2 which match the criterion.

You can use array map and array index to do:
var array1 = [{
"id": 1,
"name": "aaaaa",
"attr": [{"attr_code": "a_id", "value": "5"}]
},
{
"id": 2,
"name": "bbbbb",
"attr": [{"attr": "a_id", "value": "4"}]
}];
var array2 = [{
"id": 4,
"name": "bef",
},
{
"id": 5,
"name": "bcd",
}];
var result = array1.map(current=>{
//find index of attr in array2
let index = array2.findIndex(c=>{
if (c['id']===(Number(current['attr'][0]['value'])))
return c;
});
current["a_id"] = array2[index];
return current;
});
console.log(result);

Please check if the following code suites your requirement. You may need to make some changes.
function mergeArrays3 (arr1, arr2) {
return arr1.map((value, index) => {
let object = null;
let result = {...value};
for (let element of arr2) {
if (element.id == parseInt(value.attr[0].value)) {
object = element;
break;
}
}
if (object != null) {
let attr = value.attr[0];
if (attr.hasOwnProperty("attr")) {
result[value.attr[0].attr] = object;
} else if (attr.hasOwnProperty("attr_code")) {
result[value.attr[0].attr_code] = object;
}
}
return result;
});
}
I loop over first array and find an element in second array matching id of value.attr[0].value. If found then i added this object in the first array at key of value.attr[0].attr or value.attr[0].attr_code.

I have tried using map function on both the arrays to compare and add
the object but I didn't succeed
Below is the functional programming approach using map():
/* GIVEN */
const array1 = [{
"id": 1,
"name": "aaaaa",
"attr": [{
"attr_code": "a_id",
"value": "5"
}]
},
{
"id": 2,
"name": "bbbbb",
"attr": [{
"attr": "a_id",
"value": "4"
}]
}
]
const array2 = [{
"id": 4,
"name": "bef",
},
{
"id": 5,
"name": "bcd",
}]
/* From array2, make an object keyed by the 'id' field. We'll use this as a key-value lookup table */
const lookupTable = array2.reduce((accum, item) => {
accum[item.id.toString()] = item
return accum
}, {})
console.log('***LOOKUP TABLE***\n', lookupTable) // result is an object we use to lookup
/* From array1, we append data from the lookup table */
const final = array1.map(item => {
item.a_id = lookupTable[item.attr[0].value]
return item
})
console.log("***RESULT***\n", final)
Hope this helps.
Cheers,

Sorting JSON alphabetically by first letter

I have a JSON like this:
[
{
"id": 1,
"slug": "abakan",
"name": "Абакан"
},
{
"id": 4,
"slug": "almetevsk",
"name": "Альметьевск"
},
{
"id": 10,
"slug": "astrahan",
"name": "Астрахань"
},
{
"id": 11,
"slug": "barnaul",
"name": "Барнаул"
},
...
]
And getting this by this method:
public function getCities()
{
$cities = City::mainCities()->get(['id', 'slug', 'name']);
return response()->json($cities);
}
How can i sort this list alphabetically and with their letters. For example:
"A": [
{
"id": 1,
"slug": "abakan",
"name": "Абакан"
},
{
"id": 4,
"slug": "almetevsk",
"name": "Альметьевск"
}
],
"B": [
{
"id": 11,
"slug": "barnaul",
"name": "Барнаул"
},
...
]
and so on...
I have Laravel on the backend and VueJS on front.

My solution:
var cities = [
{ id: 1, slug: "abakan", name: "Абакан" },
{ id: 4, slug: "almetevsk", name: "Альметьевск" },
{ id: 11, slug: "barnaul", name: "Барнаул" },
{ id: 10, slug: "astrahan", name: "Астрахань" }
];
cities.sort(function(a, b) {
return a.slug[0].localeCompare(b.slug[0]);
});
var newCities = {};
for (var i = 0; i < cities.length; i++) {
var c = cities[i].slug[0].toUpperCase();
if (newCities[c] && newCities[c].length >= 0)
newCities[c].push(cities[i]);
else {
newCities[c] = [];
newCities[c].push(cities[i]);
}
}
console.log(newCities);

This works for me:
var items = [
{
"id": 11,
"slug": "barnaul",
"name": "Барнаул"
},
{
"id": 1,
"slug": "abakan",
"name": "Абакан"
},
{
"id": 4,
"slug": "almetevsk",
"name": "Альметьевск"
},
{
"id": 10,
"slug": "astrahan",
"name": "Астрахань"
}
];
var sortedItems = items.sort((a, b) => a.slug.localeCompare(b.slug));
var results = {};
for (var i = 0; i < 26; i++) {
var char = String.fromCharCode(97 + i);
var bigChar = char.toUpperCase();
results[bigChar] = [];
for (var s = 0; s < sortedItems.length; s++) {
if (sortedItems[s].slug.startsWith(char)) {
results[bigChar].push(sortedItems[s]);
}
}
}
console.log(results)

Making one to many relation array in JavaScript

I have two arrays of objects:
var a = [{
"id": 1,
"name": "q"
},
{
"id": 2,
"name": "l"
}]
and another is
var b = [{
"id": 3,
"sub": 1,
"name": "ni"
},
{
"id": 4,
"sub": 2,
"name": "bh"
}]
Here sub is the id in a
I need to have a new array which will look like this:
var c = [
{
"id":1,
"name":"q",
"map":[
{
"id":3,
"name":"ni"
}
]
},
{
"id":2,
"name":"l",
"map":[
{
"id":4,
"name":"bh"
}
]
}
]
How can I do that in JavaScript?
I am using underscore in my project.

In plain Javascript you could use Array#map, Array#forEach and a hash table.
var a = [{ "id": 1, "name": "q" }, { "id": 2, "name": "l" }],
b = [{ "id": 3, "sub": 1, "name": "ni" }, { "id": 4, "sub": 2, "name": "bh" }],
hash = Object.create(null),
result = a.map(function (a, i) {
hash[a.id] = { id: a.id, name: a.name };
return hash[a.id];
}, hash);
b.forEach(function (a) {
hash[a.sub].map = hash[a.sub].map || [];
hash[a.sub].map.push({ id: a.id, name: a.name });
}, hash);
console.log(result);
ES6
var a = [{ "id": 1, "name": "q" }, { "id": 2, "name": "l" }],
b = [{ "id": 3, "sub": 1, "name": "ni" }, { "id": 4, "sub": 2, "name": "bh" }],
hash = Object.create(null),
result = a.map((hash => a => hash[a.id] = { id: a.id, name: a.name, map: [] })(hash));
b.forEach((hash => a => hash[a.sub].map.push({ id: a.id, name: a.name }))(hash));
console.log(result);

You can do it with the help of map function and then use the find function to search the data from the other array.
var b = [{
"id": 3,
"sub": 1,
"name": "ni"
}, {
"id": 4,
"sub": 2,
"name": "bh"
}];
var a = [{
"id": 1,
"name": "q"
}, {
"id": 2,
"name": "l"
}];
var final = _.map(b, function(d) {
return {
id: d.name,
name: d.name,
map: _.find(a, function(adata) {
return adata.id == d.sub; //use underscore find to get the relevant data from array a
})
}
});
console.log(final);
<script src="https://cdnjs.cloudflare.com/ajax/libs/underscore.js/1.8.3/underscore-min.js"></script>

Nesting a parent child relationship in lodash, given the parent id and children

How would I be able to nest json object if the parent and its children was given as a property.
The data looks like:
"1": {
"id": 1,
"name": "foo",
"parent": null,
"root": 1,
"children": [2, 4, 6],
"posts":[
{ "id": "1", "name": "item1" },
{ "id": "2", "name": "item2" },
{ "id": "3", "name": "item3" }
]
},
"2": {
"id": 2,
"name": "bar",
"parent": 1,
"root": 1,
"children": null,
"posts":[
{ "id": "4", "name": "item4" }
]
},
"3": {
"id": 3,
"name": "bazz",
"parent": null,
"root": 3,
"children": [5, 7],
"posts":[
{ "id": "5", "name": "item5" },
{ "id": "6", "name": "item6" }
]
},
....
A simple groupby using lodash won't do it.
var group = _.groupBy(data, 'parent');
Here is a fiddle:
http://jsfiddle.net/tzugzo8a/1/
The context of question is a nested categories with subcategories, and categories can have categories and posts in them.
Basically I don't want to have a different property for children and posts, since they are all children of a parent.
Desired output
"1": {
"id": 1,
"name": "foo",
"parent": null,
"root": 1,
"isCategory": true,
"children": [
{
"id": 2,
"name": "bar",
"parent": 1,
"root": 1,
"isCategory": true,
"children": null
},
{ "id": "1", "name": "item1", isCategory: false },
{ "id": "2", "name": "item2", isCategory: false },
{ "id": "3", "name": "item3", isCategory: false }
]
...
}

This is my take on the question (fiddle):
var data = getData();
var group = getTree(data);
console.log(group);
function getTree(flat) {
return _.reduce(flat, function (treeObj, item, prop, flatTree) {
var children = _.map(item.children, function (childId) {
return _.set(flatTree[childId], 'isCategory', true);
}).concat(_.map(item.items, function(item) {
return _.set(item, 'isCategory', false);
}));
item.children = !!children.length ? children : null;
delete item.items;
item.parent === null && (treeObj[prop] = item);
return treeObj;
}, {});
}

Take a look on the updated fiddle:
var data = getData();
_.keys(data).forEach(function(id){
var element = data[id];
if (element.children === null){
element.children = [];
}
element.isCategory = true;
element.items.forEach(function(item){
item.isCategory = false;
})
});
_.keys(data).forEach(function(id){
var element = data[id];
element.children = element.children.map(function(childId){
return data[childId];
}).concat(element.items);
});
_.keys(data).forEach(function(id){
delete data[id].items;
});
console.log(JSON.stringify(_.findWhere(_.values(data), {'parent': null})));