sorry if this is a easy question, I am just having a hard time trying to figure out how I would tackle this problem.
For example, I have 2 Objects as below:
cont oldCar = {
model: 'Honda',
notes: {
id: 1,
timestamp: 2000,
text: 'is old'
}
}
cont oldCar = {
model: 'Toyota',
notes: {
id: 1,
timestamp: 4000,
text: 'is new'
}
}
I want to try and combine the above two objects. I know they have same key's so I wanted to merge the values of each key if they are the same. Such as:
mode: 'Honda / Toyota'
I tried the following:
let merged = {...obj1, ...obj2};
But this will merge both objects but it only retains the values from the right object. I was trying to do a for loop and add check if the key is same in both objects then combine the values together but I keep getting lost and it is hard to visualise. If someone could help me understand how i can create an for loop to start the comparison that would help me in completing the rest.
To do this merge, perhaps you could do some array-reduce, it will also work with a list of unspecific size:
let array = Array(oldCar1,oldCar2)
let result = array.reduce((a,b)=> {
let r = Object.assign({},a)
r.notes = Object.assign({},r.notes)
if (a.model != b.model) {
r["model"] = a.model + " / " + b.model;
}
if (a.notes.text != b.notes.text) {
r.notes.text = a.notes.text + " / " + b.notes.text;
}
// ...
return r;
})
What exactly do you want to achieve? Is it only the merging of model prop or something else?
Do you have more than two objects, is the amount of objects dynamic? If there are only two objects you can do that without any loops.
const merged = {
model: `${firstCar.model} / ${secondCar.model}`,
// etc...
};
But as I said before - if the amount of objects is not constant then you'd need a map that would:
go through each car
try and find a match by ID from other cars
if there's a match return a merged result, if there's no match return the object as it is
Let me know what exactly are your needs here.
Related
I am working with javascript for the first time, and I have an array of around 35000 objects, where each object looks like this:
{city: 'city1', buildingtype: 'buildingtype1', day: 1, hour: 1, energy: 59}
I want to sort this data into a "nested" JSON object, with cities as the first object. For each city, I then need to sort by buildingtype, and for each buildingtype I want an array with the energy, sorted by time.
I have added an image here which might explain it a bit better:
I have begun with something like this
let transformed_data = {}
$:{
datapoints.forEach((d)=> {
if(!(d.city in transformed_data)){
transformed_data[city] = {};
}
}
)
}
Would this be a good way to move forward?
Edit:
Thanks to some nice help this is the solution I found, where I used that the data was already sorted to my advantage.
let transformed_data = {}
$:{
datapoints.forEach((d)=> {
if(!(d.city in transformed_data)){
transformed_data[d.city] = {};
}
if (!(d.buildingtype in transformed_data[d.city])){
transformed_data[d.city][d.buildingtype] = [];
}
transformed_data[d.city][d.buildingtype].push(d.total_heating_energy)
}
)
}
The resulting object can be found here: Final_result
I have an array of countries, where each country have three properties.
const countries = [
{ name: "Poland", alpha: "POL", code: "616" },
{ name: "Hungary", alpha: "HUN", code: "348" },
// and so on...
]
Later on I want to easily access each country by any of these properties.
I was thinking of reducing this array to an object that would have three keys for each country pointing to the very same country object.
Something like this:
const countriesObject = countries.reduce((object, country) => {
const { name, alpha, code } = country;
// Create individual country object
object[name] = { ...country };
// Reference just created country object
object[code] = object[name];
object[alpha] = object[name];
return object;
});
In the end I could access each country object either by its name, code or alpha.
countriesObject["Poland"] // →
countriesObject["POL"] // → The same object
countriesObject["616"] // →
My question is, would it be considered good practice, or there are some better ways to achieve the same or similar result?
Thank you!
That's fine, as all of those keys, as you correctly noted, will be pointing to the same object. The biggest problem that I see here is that it's easy to reduce readability of the code by using this approach. Let's say we have this fragment:
console.log( countriesObject[id] );
The question is, what is id here? Is it full country name? or just alpha? or code? You might just not care, true, but if you do, consider giving them additional structure:
const countriesObject = countries.reduce((object, country) => {
const { name, alpha, code } = country;
const countryCopy = { ...country };
// it makes sense to place them on the same line to show the intent
object.name[name] = object.code[code] = object.alpha[alpha] = countryCopy;
return object;
}, { name: {}, code: {}, alpha: {} });
Another potential issue is that you won't be able to drop the countries easily from this object; it's not enough to delete just a single key pointing to it, you'll have to go and remove all three. But that doesn't seem to be a big thing here; this looks more like a dictionary.
You can indeed write it like this:
var countries = {[
"poland": {
alpha: "POL", code: "616"
},
"hungary": {
alpha: "HUN", code: "348"
}
]}
Accessing each country like this:
var poland = countries.poland;
This, in turn, produces more readable code:
var alpha = countries.poland.alpha;
instead of
var alpha = countries[0].alpha;
But there is no set preference.
Docs
I have an object that has multiple keys and each of these keys has an array storing multiple elements. I want to be able to remove a specified element from the key's array.
I have tried using the delete keyword as well as the filter method, but I have been unsuccessful. I'm a total newbie to JS so I appreciate any assistance. Also, I want to do this using ONLY JavaScript, no libraries.
Here is the code where I am creating my object:
function add(task, weekdayDue) {
let capitalWeekday = weekdayDue.charAt(0).toUpperCase() +
weekdayDue.slice(1);
if (toDoList[capitalWeekday] === undefined) {
let subArr = [];
toDoList[capitalWeekday] = subArr.concat(task);
} else {
toDoList[capitalWeekday].push(task);
}
}
and here is the code as I have it now. Clearly it is not producing the correct result:
function remove(task, weekdayDue) {
let capitalWeekday = weekdayDue.charAt(0).toUpperCase() +
weekdayDue.slice(1);
delete toDoList.capitalWeekday[task]
//the below code is working; i want to send this to another
array
if (archivedList[capitalWeekday] === undefined) {
let subArr = [];
archivedList[capitalWeekday] = subArr.concat(task);
} else {
archivedList[capitalWeekday].push(task);
}
};
add('laundry', 'monday');
add('wash car', 'monday');
add ('vacuum', 'tuesday');
add('run errands', 'wednesday');
add('grocery shopping', 'wednesday');
// the output is: { Monday: [ 'laundry', 'wash car' ],
Tuesday: [ 'vacuum' ],
Wednesday: [ 'run errands', 'grocery shopping' ] }
Then let's say I want to remove 'wash car' from Monday I was trying:
remove('wash car', 'monday');
console.log(toDoList)
// The output is an empty object {}
I personally would refactor a bit your code, but I've worked a bit around it to fix some issues.
First of all, you shouldn't use delete for your scenario, because it will reset the item at the nth position of the array with the default value, which is undefined.
Usually, for that kind of operations, since you deal with strings, you rather take a look at the first occurrence of your item in the array, take its index, and use splice (https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/splice) to actually remove the item from the array.
In this way, you end up with a clean array without invalid items in it.
Below is the working code (with the mentioned fixes) that does what you asked. As a side note, I would suggest you to avoid working with strings for such purposes, but I would rather tackle objects with unique ids, so that it's significantly easier to keep track of them between arrays and objects.
Additionally, there are some cases that you didn't think about, for instance I can think about calling remove by giving an invalid task, so you may work a bit around the code below to handle the case where taskIndex is -1 (meaning that no item was found with that index).
var toDoList = {}, archivedList = {};
function add(task, weekdayDue) {
let capitalWeekday = weekdayDue.charAt(0).toUpperCase() + weekdayDue.slice(1);
if (toDoList[capitalWeekday] === undefined) {
let subArr = [];
toDoList[capitalWeekday] = subArr.concat(task);
} else {
toDoList[capitalWeekday].push(task);
}
}
function remove(task, weekdayDue) {
let capitalWeekday = weekdayDue.charAt(0).toUpperCase() + weekdayDue.slice(1);
let taskIndex = toDoList[capitalWeekday].indexOf(task);
toDoList[capitalWeekday].splice(taskIndex, 1);
//delete toDoList[capitalWeekday][taskIndex];
if (archivedList[capitalWeekday] === undefined) {
let subArr = [];
archivedList[capitalWeekday] = subArr.concat(task);
} else {
archivedList[capitalWeekday].push(task);
}
};
add('test', 'monday');
add('wash car', 'monday');
remove('wash car', 'monday');
console.log(toDoList);
console.log(archivedList);
You are on the right path. Maybe the trouble you had with filter is because filter will return a new Array and not modify the current one. You could update your remove function and replace the line:
delete toDoList.capitalWeekday[task]
with
toDoList.capitalWeekday = toDoList.capitalWeekday.filter((item) => {return item !== task});
function remove(task, weekdayDue) {
let capitalWeekday = weekdayDue.charAt(0).toUpperCase() +
weekdayDue.slice(1);
// Assign new array with all elements but task
toDoList[capitalWeekday] = toDoList[capitalWeekday].filter(i => i !== task)
};
add('foo'...
add('bar'...
"{
"Baz": [
"Foo",
"Bar"
]
}"
remove('foo'...
"{
"Baz": [
"Bar"
]
}"
I have an array of objects. each object has a "day type"; morning, afternoon, evening. They come in random order each time I get the list due to async differences... But I need to display them in following order: morning, afternoon, evening.
If I use array.sort() they will come out in order: afternoon, evening, morning. because it sorts alphabetically right?
So... I need a compare function. but I cant figure out how to make it since all examples I have found only has two input. sort(a, b)......
day.shifts = randomOrder;
day.shifts.sort((a, b, c) => {
//some how compare all 3
}
I hope this is possible, and it is probably piece of cake.... Other wise I have thought of solutions like so
day.shifts = randomOrder;
const morning = [];
const afternoon = [];
const evening = [];
day.shifts.forEach(shift => {
if(shift.type === 'morning'){
morning.push(shift)
}
if(shift.type === 'afternoon'){
afternoone.push(shift)
}
if(shift.type === 'evening'){
evening.push(shift)
}
}
day.shifts = morning.concat(afternoon).concat(evening);
I would prefer a compare method if that is possible. Or at least something a bit more "pretty" than my split to separate arrays and the concatenate method...
the objects in the list looks like this:
{
type: 'morning',
name: 'some person',
id: 'person db index',
}
You can sort them like this:
const order = ["morning", "afternoon", "evening"];
day.shifts.sort((a, b) => order.indexOf(a.type) - order.indexOf(b.type));
That basically sorts the shifts after wich type comes first in the order array.
You could sort by type with an object for the order.
var types = { morning: 1, afternoon: 2, evening: 3 };
day.shifts.sort((a, b) => types[a.type] - types[b.type]);
I would like to store product information in a key, value array, with the key being the unique product url. Then I would also like to store the visit frequency of each of these products. I will store these objects as window.localStorage items, but that's not very important.
The thing I had in mind was two key value arrays:
//product information
prods["url"] = ["name:product_x,type:category_x,price:50"]
//product visits frequency
freq["url"] = [6]
Then I would like to sort these prods based on the frequency.
Is that possible?
Hope you guys can help! Thanks a lot
Well you seem to have made several strange choices for your data format/structure. But assuming the format of the "prod" is beyond your control but you can choose your data structure, here's one way to do it.
Rather than two objects both using url as a key and having one value field each I've made a single object still keyed on url but with the product and frequency information from each in a field.
Objects don't have any inherent order so rather than sorting the table object I sort the keys, your "url"s ordered by ascending frequency.
To show that it's sorted that way I print it out (not in the same format).
For descending frequency, change data[a].freq - data[b].freq to data[b].freq - data[a].freq
var data = {
"url": {
prod: "name:product_x,type:category_x,price:50",
freq: 6
},
"url2": {
prod: "name:product_y,type:category_y,price:25",
freq: 3
}
};
var sorted = Object.keys(data).sort((a, b) => data[a].freq - data[b].freq);
console.log(sorted.map(k => [data[k].freq, k, data[k].prod]));
There's more than one way to format the data, which would change the shape of the code here.
maybe something like this:
var prods = [
{url:1, val:[{name:'a',type:'x',price:60}]},
{url:2, val:[{name:'b',type:'x',price:30}]},
{url:3, val:[{name:'c',type:'x',price:50}]},
{url:4, val:[{name:'c',type:'x',price:20}]},
{url:5, val:[{name:'c',type:'x',price:10}]},
{url:6, val:[{name:'c',type:'x',price:40}]}
];
var freq = [
{url:1, freq:6},
{url:2, freq:3},
{url:3, freq:5},
{url:4, freq:2},
{url:5, freq:1},
{url:6, freq:4}
];
prods.sort(function (a, b) {
var aU = freq.filter(function(obj) {
return obj.url === a.url;
});
var bU = freq.filter(function(obj) {
return obj.url === b.url;
});
if (aU[0].freq > bU[0].freq) {
return 1;
}
if (aU[0].freq < bU[0].freq) {
return -1;
}
return 0;
});