I am trying to access a nested object in ReactJS. This is what the object looks like:
const characteristics = [
{ id: "geo", content: 'Geopolitical' },
{ id: "dog", content: 'Dog Loving' },
];
const starterColumns = {
"1": {
name: 'I am',
items: characteristics
},
"2": {
name: 'fullstack developer',
items: []
}
}
const [columns, setColumns] = useState(starterColumns);
This is the error I get when I try to console.log(columns['2']['items']['0']['id']):
TypeError: Cannot read property 'id' of undefined
Does this have to do with the fact that I am working with a stateful variable? Is something funky going on with the nested objects? Thanks for the help!
EDIT
The problem was that there was no object in the column so I had no object to access. Now the problem outstanding is how do I fill that void without displaying a new drag and drop piece. Thanks for helping!
EDIT
I used a try/catch statement to check the object so if it is empty, nothing happens.
Use try catch only for errors that you can't handle
To access an element use dot notation whenever it's possible instead of using bracket notation []
When there is an empty array in the items you can't access to the id you will get an error so the solution is to check if the array is not empty
columns['2'].items.length > 0
To access the first element of an array you have to use [0] instead of ['0']
try this solution
if (columns['2'].items.length > 0) {
console.log(columns['2'].items[0].id)
}
Related
I'm looking for a way to access a nested array in my data structure.
My objects in my data array look like this :
{
name: name,
logo: url,
categories: [
{
name: Entertainment,
slug: "entertainment
},
{
name: Kids,
slug: kids
},
]
}
In the Docs I states that I need to use columnHelper.accessor to extract primitive values for each item in your data array.
My question is : how can I configure my accessor on "categories" to display both of them in my cell (using map I guess) ?
First, you don't need to use columnHelper; you can, for convenience (well, type safety, mostly).
You can do something like this:
cell: info => {
const value = info.getValue() as YourCategoryType[]; //casting may not be required here
return <>{value.map(v => <p key={v.slug}>{v.name}</p>)}</>
},
I am having trouble with writing the following method on an Angular class. I don't know how to add values from arrayId to the data array in the series object.
getChartOptions() {
const arrayId=[];
const arrayTimestamp=[];
const arrayData=[];
const arrayData2=[];
var i=0;
this.httpClient.get<any>('http://prod.kaisens.fr:811/api/sleep/?deviceid=93debd97-6564-454b-be33-35bd377a2563&startdate=1612310400000&enddate=1614729600000').subscribe(
reponse => {
this.sleeps = reponse;
this.sleeps.forEach(element => { arrayId.push(this.sleeps[i]._id),arrayTimestamp.push(this.sleeps[i].timestamp),arrayData.push(this.sleeps[i].data[18]),arrayData2.push(this.sleeps[i].data[39])
i++;
});
console.log(arrayId);
console.log(arrayTimestamp);
console.log(arrayData);
console.log(arrayData2);
}
)
return {
series: [{
name: 'Id',
data: [35, 65, 75, 55, 45, 60, 55]
}]
}
}
I have two main pieces of advice for you:
Know the types of that data that you are dealing with.
Get familiar with all of the various array methods.
get<any>() is not a helpful type. If you understand what the response is then Typescript can help ensure that you are handling it correctly.
I checked out the URL and it looks like you get an array of objects like this:
{
"_id": 4,
"device_id": "93debd97-6564-454b-be33-35bd377a2563",
"timestamp": 1612310400000.0,
"data": "{'sleep_quality': 1, 'sleep_duration': 9}"
},
That data property is not properly encoded as an object or as a parseable JSON string. If you control this backend then you will want to fix that.
At first I thought that the data[18] and data[39] in your code were mistakes. Now I see that it as attempt to extract values from this malformed data. Accessing by index won't work if these numbers can be 10 or more.
The type that you have now is:
interface DataPoint {
_id: number;
device_id: string;
timestamp: number;
data: string;
}
The type that you want is:
interface DataPoint {
_id: number;
device_id: string;
timestamp: number;
data: {
sleep_quality: number;
sleep_duration: number;
}
}
You can type the request as this.httpClient.get<DataPoint[]>( and now you'll get autocomplete on the data.
It looks like what you are trying to do is basically to convert this from one array of rows to a separate array for each column.
You do not need the variable i because the .forEach loop handles the iteration. The element variable in the callback is the row that you want.
this.sleeps.forEach(element => {
arrayId.push(element._id);
arrayTimestamp.push(element.timestamp);
arrayData.push(element.data[18]);
arrayData2.push(element.data[39]);
});
The .forEach loop that you have now is efficient because it only loops through the array once. A .map for each column is technically less efficient because we have to loop through separately for each column, but I think it might make the code easier to read and understand. It also allows Typescript to infer the types of the arrays. Whereas with an empty array you would need to annotate it like const arrayId: number[] = [];.
const mapData = (response: DataPoint[]) => {
return [{
name: 'Id',
data: response.map(element => element._id)
}, {
name: 'Timestamp',
data: response.map(element => element.timestamp)
}, {
name: 'Sleep Quality',
data: response.map(element => parseInt(element.data[18])) // fix this
}, {
name: 'Sleep Duration',
data: response.map(element => parseInt(element.data[39])) // fix this
}]
}
The HTTP request is asynchronous. If you access your array outside of the subscribe callback then they are still empty. I'm not an angular person so this part I'm unsure of, but I think that you want to be updating a property on your class instead of returning the value?
Just follow this piece of code:
series: [{
name: 'Id',
data: arrayId
}]
I'm stuck since a while trying to access a nested array inside another array after filtering it by an id. To be clear, this is the mock data I have:
bundleSets: [
{
id: 1,
title: "bundle set 1",
bundles: [
{
bundleTitle: "bundle 1",
content:[]
},
{
bundleTitle: "bundle 2",
content:[]
}
]
},
{ id:2,
title: "bundle set 2",
bundles: [
{bundleTitle: "ciaopao", content:[]}
]
},
{ id:3,
title: "bundle set 3",
bundles: [
{bundleTitle: "ciapo", content:[]}
]
}
]
Now I need to filter each bundleSets by id, and then access the bundles array inside and mapping those elements. This is what I tried to do:
const [key,setKey]=useState(1)
const [bundles,setBundles]=useState([])
useEffect(()=>{
const filteredBundles = bundleSets && bundleSets.filter(bundleSet=>bundleSet.id==key).map(filteredBundles=>{
return filteredBundles.bundles
})
setBundles(filteredBundles)
},[key])
Now If I try mapping the new state I can see on the console.log a weird [Array(1)] instead of the usual [{}] and I can't render it to the page. Where am I getting wrong with this?
Array.prototype.map returns an array and the callback you're passing to the map method returns filteredBundles.bundles which is an array. So, you get an array of arrays. filteredBundles is a confusing name, btw.
Since you're looking up the bundle by id and the ids are unique in the bundleSets array, you can use Array.prototype.find to find the bundle set by id and then get the bundle array. You can return an empty array if find returns undefined (if the key is not found).
const bundles = bundleSets?.find(set => set.id === key)?.bundles || []
I understand the source of the problem, but I'm just a bit stuck on how to resolve it.
I'm doing something like items.map(item, index), but in the browser console I get an entire object. This object has another object within it called data, and that's where I'm trying to apply the map function, since I understand it only works on arrays. The object looks like this:
{
"data":[
{"id":"1","name":"a","description":"aaaaaa"},
{"id":"2","name":"b","description":"bbbbbb"},
{"id":"3","name":"c","description":"cccccc"}
]
}
But when I try to do items.data.map, I get the error property 'data' does not exist on type 'Item[]', which is true. It only shows up in the browser console.
What am I missing and is it possible to resolve it without adding a data property?
Thank you!
data is an array, so to access its inner content, you have to apply map() in a nested manner:
items.map((item) => item.data.map((data) => /* you can access the inner data here */));
items.data.map doesn't work because the key is "data", not data
Your object keys should not be strings:
{
data: [
{id: 1, name: "a", description: "aaaaaa"},
{id: 2, name: "b", description: "bbbbbb"},
{id: 3, name: "c", description: "cccccc"}
]
}
Then you can do:
items.data.map((item, index) => ...
I have an array that looks like this:
[{
LocalBond:"0",
LocalCash:"2.42",
LocalEquity:"0",
ForeignEquity: "4",
...
}]
What I want it look like:
[{
Source: "LocalBond",
Value: "0"
},
Source: "LocalCash",
Value: "2.42"
},
Source: "LocalEquity",
Value: "0"
},
{...}
]
I want to turn a single object into many objects. I also need the exclude the 'ForeignEquity' result.
I tried using _.map, and returning the fields I want, but I am struggling a bit. Am I on the right track? When I pass more than one parameter into my function, I don't get the desired result.
The most simple code is pure javascript:
Using for..in access to the property of the object, and inside of the for loop build the array.
http://www.w3schools.com/jsref/jsref_forin.asp
Example:
https://jsfiddle.net/jewrsL8a/5/
var collection = [{
LocalBond:"0",
LocalCash:"2.42",
LocalEquity:"0",
ForeignEquity: "4"
}];
var result = [];
for (var property in collection[0]) {
if(property!=='ForeignEquity'){
result.push({'Source': property, 'Value': collection[0][property]});
}
}
console.log(result);