in this sample using reduce on array of objects works fine but when i insert it all into a function it starts to return undefined... it probably has to do with me not understanding how returning stuff from functions works
const egArrOfObj = [
{
name:'tomato',
},
{
name:'potato',
},
];
console.log(
egArrOfObj
.reduce((acc, curr) => {
return [...acc, curr.name]
} ,[] )
);
const namesFunction = (arrOfObj) => {
arrOfObj
.reduce((acc, curr) => {
return [...acc, curr.name]
} ,[] )
};
const names = namesFunction(egArrOfObj);
console.log(names)
If you add the return statement into your function then it will work as well.
Like the following:
const egArrOfObj = [{
name:'tomato',
},
{
name:'potato',
}];
const namesFunction = (arrOfObj) => {
return arrOfObj.reduce((acc, curr) => {
return [...acc, curr.name]
}, [])
};
console.log(namesFunction(egArrOfObj));
I hope that helps!
Related
I'm trying to map the JSON from the URL to an array but I think my mapping of the data isn't correct. I want to find every value inside of attributes and count how many instances of each value there are in the JSON file/ array.
[
{
name: "1",
attributes: [
{
trait_type: "hat",
value: "blue"
},
{
trait_type: "hair",
value: "red"
}
]
}
];
$.getJSON(
"https://jsonware.com/api/v1/json/3c53cbcd-5351-4fba-8b89-5f1fb009e857",
function (data) {
var items = $.map(data.attributes, function (i) {
return i.value;
const result = data.reduce(
(acc, curr) => ((acc[curr] = (acc[curr] || 0) + 1), acc),
{}
);
console.log(result);
console.log(items);
});
}
);
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
It is not clear what you want from the call.
There will me no code run after return i.value; so the console.logs will not run
The values you are getting cannot be added.
Here I get an array of all values. jQuery not needed
fetch(
"https://jsonware.com/api/v1/json/3c53cbcd-5351-4fba-8b89-5f1fb009e857")
.then(response => response.json())
.then(data => {
const values = Object.values(data).flatMap(item => ({[item.name]:item.attributes.map(attr => attr.value )}))
values.forEach(val => console.log(Object.keys(val)[0],Object.values(val)[0].length))
const allValues = Object.values(data).map(item => item.attributes.map(attr => attr.value ))
console.log("All values: ",allValues.length,allValues)
}
);
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
I can't figure out how I can change :
{"first":["de"], "second":["ab","de"], "third":["de"]}
to:
{"de":["first", "second", "third"], "ab":["second"]}
I want to associate unique values with list of containing keys. What I tried(but I think I'm far from it):
const data = {
"first":["de"],
"second":["ab","de"],
"third":["de"]
}
console.log(
Object
.keys(data).reduce(function(obj, key) {
obj[data[key]] = key;
return obj;
}, {})
)
Thanks for your help!
Object.entries to get it into an array, reduce to build the new object, and forEach to loop over the array
const o = {"first":["de"], "second":["ab","de"], "third":["de"]}
const result = Object.entries(o).reduce((obj, [key, arr])=>{
arr.forEach(lng => {
obj[lng] = obj[lng] || [];
obj[lng].push(key);
})
return obj
}, {});
console.log(result);
You have to loop the array and for each item in the array check if an array for that value exists in the accumulator or not before adding it:
let result = Object.entries(data).reduce((acc, [key, arr]) => { // for each key-array of the original object
arr.forEach(value => { // for each value in the array
acc[value] = acc[value] || []; // create an array in the output object if it doesn't already exist
acc[value].push(key); // push the key to it
});
return acc;
}, {});
I also used Object.entries with each entry desctuctured as [key, arr] so I don't have to use the extra [key] to get the array while using Object.keys.
Demo:
let data = {"first":["de"], "second":["ab","de"], "third":["de"]};
let result = Object.entries(data).reduce((acc, [key, arr]) => {
arr.forEach(value => {
acc[value] = acc[value] || [];
acc[value].push(key);
});
return acc;
}, {});
console.log(result);
On reduce callback, data[key] is an array of string values. So it is needed to loop that data[key] array values and assign value for each array item.
const data = {
"first":["de"],
"second":["ab","de"],
"third":["de"]
}
console.log(
Object.keys(data).reduce(function(obj, key) {
data[key].forEach((val) => {
obj[val] ? obj[val].push(key) : obj[val] = [ key ];
});
return obj;
}, {})
)
Try this (naive solution), if this works for you
const data = { first: ["de"], second: ["ab", "de"], third: ["de"] };
let dataMap = new Map();
Object.keys(data).forEach((key) => {
data[key].forEach((val) => {
if (dataMap.has(val)) {
dataMap.set(val, [...dataMap.get(val), key]);
} else {
dataMap.set(val, [key]);
}
});
});
let nData = [];
dataMap.forEach((value, key) => {
nData.push({
[key]: value
});
});
console.log(nData);
You could take a double reduce with the entries.
const
data = { first: ["de"], second: ["ab", "de"], third: ["de"] },
result = Object
.entries(data)
.reduce((o, [value, keys]) => keys.reduce((q, key) => {
(q[key] ??= []).push(value);
return q;
}, o), {});
console.log(result);
I'm not using reduce but here's a "bruteforce" for your problem which works:
res = {};
Object.keys(data).forEach(key => {
data[key].forEach(el => {
if (! res[el])
res[el] = [];
if (! res[el].includes(key))
res[el].push(key);
})
});
I am outputting the matched value of projects when the name of my logo matches the items object within projects with the help of a reduce function. However, whenever I click on multiple logos that both match project.items I am rendering duplicates.
Here is my code:
logos.reduce((acc, logo) => {
if (logo.active) {
Object.values(projects).forEach((proj) => {
if (Object.values(proj.items).includes(logo.name)) {
console.log(acc)
acc.push((<Project title={proj.title} routeName={proj.routeName} items={proj.items} description={proj.description}/>));
}
});
}
return acc
}, [])
My first idea was to create another array, run a for loop and iterate through the values like: filteredValues[i].props.title and push the contents of that loop to an array. I ran run a reduce on that array like this but I was not able to eliminate the duplicate:
const filteredArr = arr.reduce((acc, current) => {
const x = acc.find(item => item.title === current.title);
if (!x) {
return acc.concat([current]);
} else {
return acc;
}
}, []);
Anyway, here's the output of acc which I am using to render my Project component
May be below code is what you need.
const filteredArr = this.getUnique(arr, 'title');
getUnique(arr, comp) {
const unique = arr.map(e => e[comp]).map((e, i, final) => final.indexOf(e) === i && i).filter((e) => arr[e]).map(e => arr[e]);
return unique;
}
Steps involve is to:
Store the comparison values in array "arr.map(e => e[comp])"
Store the indexes of the unique objects ".....).map((e, i, final) => final.indexOf(e) === i && i)"
Eliminate the false indexes & return unique objects ".....).filter((e) => arr[e]).map(e => arr[e])"
You can write your original loop like this
logos
.reduce((acc, logo) => {
if (logo.active) {
Object.values(projects).forEach((proj) => {
if (
Object.values(proj.items).includes(logo.name) &&
!acc.find((item) => item.value === logo.name)
) {
console.log(acc);
acc.push({
value: logo.name,
component: (
<Project
title={proj.title}
routeName={proj.routeName}
items={proj.items}
description={proj.description}
/>
),
});
}
});
}
return acc;
}, [])
.map((values) => values.component);
You can use the Map object to filter out duplicates.
let arrFiltered = [];
// form map of unique arr items
const arrMap = new Map();
arr.forEach(item => arrMap.set(item.title, item));
// form array of all items in map
arrMap.forEach(item => arrFiltered.push(item));
I had to run a reduce function outside of the original forEach loop and check those values with a some function.
logos.reduce((acc, logo) => {
if (logo.active) {
Object.values(projects).forEach((proj) => {
if (Object.values(proj.items).includes(logo.name)) {
console.log(acc)
acc.push((<Project title={proj.title} routeName={proj.routeName} items={proj.items} description={proj.description}/>));
}
});
acc = acc.reduce(function (p, c) {
if (!p.some(function (el) { return el.props.title === c.props.title; })) p.push(c);
return p;
}, []);
}
return acc
}, [])
I need to return an additional value other than Observable, key string from flatMap from below setup:
this.subscribeInit = this.tradingService.getInProgress()
.pipe(flatMap((s) => {
this.keys = s.map((tdi) => tdi.key);
return this.keys;
}),
flatMap((key) =>{
var res = this.tradingService.getTradingData(key);//returns `Observable<any>`
return res;
}))
.subscribe(res => {
console.log('Key is : ' + res.key);
},
undefined,
() => this.onComplete());
Something like:
flatMap((key) =>{
var res = this.tradingService.getTradingData(key);
return {res,key};
}))
How to achieve this?
Just use map ...
flatMap((key) =>{
return this.tradingService.getTradingData(key).pipe(map((res) => {
return {res,key};
}));
}))
ps: i am a bit confused: isnt flatMap deprecated and replaced my mergeMap, switchMap, ... ?
edit: apparently the problem was caused by using flatMap instead of mergeMap.
You can destructur object as function parameters
this.subscribeInit = this.tradingService.getInProgress()
.pipe(flatMap((s) => {
this.keys = s.map((tdi) => tdi.key);
return this.keys;
}),
flatMap((key) =>{
var res = this.tradingService.getTradingData(key);
return {res,key}; // pack res and key into object
}))
.subscribe(({res,key}) => { // destructuring previously returned object
console.log('Key is : ' + res[key]);
},
undefined,
() => this.onComplete());
const val1 = 'some val1', val2 = 'some val2';
Promise.resolve({val1, val2}).then(({val1, val2}) => {
console.log(val1);
console.log(val2);
});
Is there a more elegant way then this to execute several functions in succession for each item in the array:
type Transform<T> = (o: T) => T;
type Item = { /* properties */ };
transform(input, transformers: Transform<Item>[]) {
const items: Item[] = getItems(input);
return items.map(item => {
let transformed = item;
tramsformers.forEach(t => transformed = t(transformed));
return transformed;
})
}
This is a great use case for reduce:
transform(input, transformers: Transform<Item>[]) {
const items: Item[] = getItems(input);
return items.map(item => transformers.reduce((val, transformer) => transformer(val), item));
}
Or perhaps more readably:
transform(input, transformers: Transform<Item>[]) {
const items: Item[] = getItems(input);
return items.map(
item => transformers.reduce(
(val, transformer) => transformer(val),
item
)
);
}
Live Example:
function getItems(input) {
return [
"abcdefg",
"1234567"
];
}
function transform(input, transformers) {
const items = getItems(input);
return items.map(item => transformers.reduce((val, transformer) => transformer(val), item));
}
const result = transform("x", [
v => v.toUpperCase(),
v => v.substring(1, v.length - 1)
]);
console.log(result);
As Nitzan Tomer points out, we could do away with the items constant:
transform(input, transformers: Transform<Item>[]) {
return getItems(input).map(
item => transformers.reduce(
(val, transformer) => transformer(val),
item
)
);
}
I frequently keep those sorts of things for debugging, but some good debuggers now make it easy to see the return value of functions before they return (Chrome's does), so if you removed it, you could step into getItems to see the items before the map.
Here's a bit more reusable version, based on #T.J.Crowder's answer:
export type Transform<T> = (o: T) => T;
export function pipe<T>(sequence: Transform<T>[] = []) {
return (item: T) => sequence.reduce((value, next) => next(value), item);
}
transform(input, transformers?) {
return getItems(input).map( pipe(transformers) );
}
Note that type is inferred from getItems(input) and return type is transform(): Item[].