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How to iterate json object field in react

There is a JSON for categories with the following structure
[
{
"category": "Mobiles",
"sub": [
{
"name": "Apple"
},
{
"name": "Samsung"
}
]
},
{
"category": "Televisions",
"sub": [
{
"name": "Lg"
},
{
"name": "Sony"
}
]
}
]
First i load data from backend to a variable called categories (On the backend side im using expressjs and pass data with res.json(JSON.parse(fs.readFileSync('categories.json')))
I want to iterate through categories sub category with
{categories.map(function (category, i) {
return (
<>
<h6 Key={i}>{category.category}</h6> //For example: <h6>Mobiles</h6>
<>... [logic to iterate the current category's sub categories] ...</> //For example: <p>Apple</p> <p>Samsung</p>
</>
);
})}
I tried to use a second map on category.sub like category.sub.map((s,j)=><p Key={j}>{s.name}</p>) but unfortunely i can't get it work, and I can't describe my problem to Google in English so it can be an easy answer and i am the big L
Any help?
Thanks

Try this, uncomment out the console.log to verify data if screen is white.
return (
<>
{categories.map(function (category, i) {
// console.log(category.category );
// console.log(category.sub );
return (
<>
<h6 key={i}>{category.category}</h6>
<>
{category.sub.map(function (sub, j) {
// console.log(category.category + '' + sub.name);
return <p key={j}> {sub.name}</p>;
})}
</>
</>
);
})}
</>
);
Data:
let categories = [
{
category: 'Mobiles',
sub: [
{
name: 'Apple',
},
{
name: 'Samsung',
},
],
},
{
category: 'Televisions',
sub: [
{
name: 'Lg',
},
{
name: 'Sony',
},
],
},
];

Join multiple array maps in ReactJs

im new in reactjs, is that possible to do in reactjs,like mysql inner join, here my sample code.
{dataCustomer.map((customer) => (
<tr>
<td>{customer.custid}</td>
<td>{customer.custname}</td>
<td>{customer.mailingaddr}</td>
<td>{customer.stateid}</td>
<td>{customer.districtid}</td>
<td>{customer.postcode}</td>
</tr>
))}
{dataState.map((state) => (
<tr>
<td>{state.stateid}</td>
<td>{state.statename}</td>
</tr>
))}
how to join array map data from customer.stateid & state.stateid to call state.statename without use SQL syntax?..Is that possible?

This should work
let joinedData=[]
dataCustomer.forEach((customer)=>{
let st= dataState.filter((state)=>state.stateid===customer.stateid);
if(st.length>0)
joinedData.push({...customer,statename:st[0].statename})
})
joinedData array will now contain the customer objects with the corresponding statename and you can use it as
{joinedData.map((customer) => (
<tr>
<td>{customer.custid}</td>
<td>{customer.custname}</td>
<td>{customer.mailingaddr}</td>
<td>{customer.stateid}</td>
<td>{customer.districtid}</td>
<td>{customer.postcode}</td>
<td>{customer.statename}</td>
</tr>
))}

It is not exactly the same but I think the function below that I wrote can help you:
let customers = [{
name: "Foo",
stateid: 1
},
{
name: "Boo",
stateid: 3
},
{
name: "Goo",
stateid: 2
},
{
name: "Zoo",
stateid: 2
},
];
let states = [{
name: "State1",
id: 1
},
{
name: "State2",
id: 2
},
];
function join(customers, states, column1, column2) {
return customers.map(customer => {
states.forEach(state => {
if (customer[column1] === state[column2]) {
customer["state"] = { ...state };
}
})
return customer;
})
}
console.log(join(customers, states, "stateid", "id"))
Note that column1 and column2 parameters are the properties you are joining on.

Loop inside loop in redux store

I have a simple state:
const INITIAL_PEOPLE = {
name: 'Friends',
list: [
{
id: 1,
name: 'Alexander',
child: [
{
id: 2,
name: 'Romuald'
},
{
id: 3,
name: 'Vanessa'
}
]
},
{
id: 4,
name: 'Alex',
child: [
{
id: 5,
name: 'Jessica'
}
]
}
]
}
Now I want to print that. Look at my code
{prople.list.map(person =>
<li key={person.id}>{person.name}
{person.child.map(child =>
{child.name}
)}
</li>
)}
First loop works correctly but if I added second loop (child), console catch an error that person.child is undefined. Why it doesn't work?

You were not returning any value from your map function.
{INITIAL_PEOPLE.list.map((person) => {
return (
<li key={person.id}>
{person.name}
{person.child.map((child) => {
return child.name;
})}
</li>
);
})}

Your code should be written like this with a check if person have a child array.
{prople.list.map(person =>
<li key={person.id}>{person.name}
{person.child && person.child.length && person.child.map(child =>
{return child.name }
)}
</li>
)}
Here before calling the map function for child, we are checking if person has an attribute named child and if child is an array by checking if child has a property length by person.child.length. Notice the return part in the nested map.

Issues with an object- Will not map

Whenever I run my React program, I receive the following error:
Objects are not valid as a React child (found: object with keys {mappedCats}). If you meant to render a collection of children, use an array instead.
in choicesList (at App.js:33)
What I am trying to do is take the FEATURES object, iterate through it and create a div for each category. Then iterate through the items of that category to show the name and cost of each item. I tried converting the object to an array, but it doesn't seem to be working. Originally I tried splitting this up into multiple components but I think I was overly ambitious.
The Categories component just takes the props and puts them into a div and paragraphs.
If somebody could point out my mistake I would appreciate it. Thank You
import React from 'react'
import Categories from './categories'
const choicesList = (props) => {
const FEATURES = {
Processor: [
{
name: '17th Generation Intel Core HB (7 Core with donut spare)',
cost: 700
},
{
name: 'Professor X AMD Fire Breather with sidewinder technology',
cost: 1200
}
],
"Operating System": [
{
name: 'Ubuntu Linux 16.04',
cost: 200
},
{
name: 'Bodhi Linux',
cost: 300
}
],
"Video Card": [
{
name: 'Toyota Corolla 1.5v',
cost: 1150.98
},
{
name: 'Mind mild breeze 2000',
cost: 1345
}
],
Display: [
{
name: '15.6" UHD (3840 x 2160) 60Hz Bright Lights and Knobs',
cost: 1500
},
{
name: '15.3" HGTV (3840 x 2160) Home makeover edition',
cost: 1400
},
]
};
const mappedCats = Object.keys(FEATURES).map((cat) => {
return (
<div>
<h1>{cat}</h1>
{Object.keys(FEATURES[cat]).map((item, idx) => {
return (
<Categories name={FEATURES[cat][idx].name} cost={FEATURES[cat][idx].cost}/>
)
})}
</div>
)
})
return(
{mappedCats}
)
}
export default choicesList

Because React components must render a single root element, you'd need to wrap it in either a fragment or an element:
return (
<>{ mappedCats }</>
)
As raw js (not enclosed in markup) your render method is returning an object literal:
// this is shorthand for { mappedCats: mappedCats }
return { mappedCats };

mappedCats itself is a valid element(s). Just return that
return mappedCats
const ChoicesList = (props) => {
const FEATURES = {
Processor: [
{
name: "17th Generation Intel Core HB (7 Core with donut spare)",
cost: 700,
},
{
name: "Professor X AMD Fire Breather with sidewinder technology",
cost: 1200,
},
],
"Operating System": [
{
name: "Ubuntu Linux 16.04",
cost: 200,
},
{
name: "Bodhi Linux",
cost: 300,
},
],
"Video Card": [
{
name: "Toyota Corolla 1.5v",
cost: 1150.98,
},
{
name: "Mind mild breeze 2000",
cost: 1345,
},
],
Display: [
{
name: '15.6" UHD (3840 x 2160) 60Hz Bright Lights and Knobs',
cost: 1500,
},
{
name: '15.3" HGTV (3840 x 2160) Home makeover edition',
cost: 1400,
},
],
};
const mappedCats = Object.keys(FEATURES).map((cat) => {
return (
<div>
<h1>{cat}</h1>
{Object.keys(FEATURES[cat]).map((item, idx) => {
return (
<div>
{`name: ${FEATURES[cat][idx].name}`}
<br></br>
{`cost: ${FEATURES[cat][idx].cost}`}
</div>
);
})}
</div>
);
});
return mappedCats;
//return (<div>{ mappedCats }</div>);
};
const domContainer = document.querySelector('#app');
ReactDOM.render(<ChoicesList />, domContainer);
<script crossorigin src="https://unpkg.com/react#16/umd/react.production.min.js"></script>
<script crossorigin src="https://unpkg.com/react-dom#16/umd/react-dom.production.min.js"></script>
<div id="app"> </div>

React mapping menu from JSON

I have a scrolling menu items, and the titles of each item is hardcoded into a const, along side with the id
const list = [
{ name: "category1", id: 0 },
{ name: "category2", id: 1 },
{ name: "category3", id: 2 },
{ name: "category4", id: 3 },
{ name: "category5", id: 4 },
{ name: "category6", id: 5 },
{ name: "category7", id: 6 },
{ name: "category8", id: 7 }
];
I have a json file that contains the category name for each child:
{
"results": [
{
"category": "category1",
"name": {
"title": "mr",
"first": "ernesto",
"last": "roman"
},
"email": "ernesto.roman#example.com",
"id": {
"name": "DNI",
"value": "73164596-W"
},
"picture": {
"large": "https://randomuser.me/api/portraits/men/73.jpg",
"medium": "https://randomuser.me/api/portraits/med/men/73.jpg",
"thumbnail": "https://randomuser.me/api/portraits/thumb/men/73.jpg"
}
},
{
"category": "category2",
"name": {
"title": "mr",
"first": "adalbert",
"last": "bausch"
},
"email": "adalbert.bausch#example.com",
"id": {
"name": "",
"value": null
} etc....
I want to show these categories "category": "category1", as the titles of my menu, I now that I need to start stateless and add them from the JSON, the fetching part from the JSON is done locally in componentDidMount, but I am not sure how can I map them into appearing as menu names to make the menu dynamic, I basically want the same output but from the json not hardcoded. here is a sandbox snippet, would appreciate the help.
https://codesandbox.io/s/2prw4j729p?fontsize=14&moduleview=1

Just convert the JSON output to an object like list with a map function from the results and then set is as MenuItems on the state, which is what you pass to the function on render(). Like that.
import React, { Component } from "react";
import ScrollMenu from "react-horizontal-scrolling-menu";
import "./menu.css";
// One item component
// selected prop will be passed
const MenuItem = ({ text, selected }) => {
return (
<div>
<div className="menu-item">{text}</div>
</div>
);
};
// All items component
// Important! add unique key
export const Menu = list =>
list.map(el => {
const { name, id } = el;
return <MenuItem text={name} key={id} />;
});
const Arrow = ({ text, className }) => {
return <div className={className}>{text}</div>;
};
export class Menucat extends Component {
state = {
selected: "0",
MenuItems: []
};
componentDidMount() {
fetch("menu.json")
.then(res => res.json())
.then(result => {
const items = result.results.map((el, idx) => {
return { name: el.category, id: idx };
});
this.setState({
isLoaded: true,
MenuItems: items
});
});
}
render() {
const { selected, MenuItems } = this.state;
// Create menu from items
const menu = Menu(MenuItems, selected);
return (
<div className="App">
<ScrollMenu
data={menu}
selected={selected}
onSelect={this.onSelect}
alignCenter={true}
tabindex="0"
/>
</div>
);
}
}
export default Menucat;
Cheers!

Looks like you don't have to hard code your category list at all. In your componentDidMount() fetch the json and group the results into separate categories like this:
const json = {
"results": [
{
category: "category1",
name: "Fred"
},
{
category: "category1",
name: "Teddy"
},
{
category: "category2",
name: "Gilbert"
},
{
category: "category3",
name: "Foxy"
},
]
}
const grouped = json.results.reduce((acc, cur) => {
if (!acc.hasOwnProperty(cur.category)) {
acc[cur.category] = []
}
acc[cur.category].push(cur)
return acc;
}, { })
// parent object now has 3 properties, namely category1, category2 and category3
console.log(JSON.stringify(grouped, null, 4))
// each of these properties is an array of bjects of same category
console.log(JSON.stringify(grouped.category1, null, 4))
console.log(JSON.stringify(grouped.category2, null, 4))
console.log(JSON.stringify(grouped.category3, null, 4))
Note that this json has 4 objects in result array, 2 of cat1, and 1 of cat 2 and cat3. You can run this code in a separate file to see how it works. Ofcourse you will be fetching the json object from server. I just set it for demonstration.
Then set teh state:
this.setState({ grouped })
Then in render() you only show the categories that have items like:
const menuBarButtons = Object.keys(this.state.grouped).map((category) => {
/* your jsx here */
return <MenuItem text={category} key={category} onClick={this.onClick} blah={blah}/>
/* or something , it's up to you */
})
I'm assuming you're showing the items based on the currently selected category this.state.selected. So after you have rendered your menu, you would do something like:
const selectedCatItems = this.state.grouped[this.state.selected].map((item) => {
return <YourItem name={item.name} key={item.id} blah={blah} />
})
Then render it:
return (
<div className="app">
<MenuBar blah={blah}>
{menuBarButtons}
</Menubar>
<div for your item showing area>
{selectedCatItems}
</div>
</div>
)
Also, don't forget to change your onClick() so that it sets this.state.selected state properly. I believe you can figure that out yourself.
Hope it helps.
PS: I didn't write a whole copy/paste solution to your problem simply because I'm reluctant to read and understand your UI details and the whole component to component data passing details..