I am in the freeCodeCamp Use the reduce Method to Analyze Data challenge.
I tried:
function getRating(watchList){
// Add your code below this line
var count = 0;
var sum = 0;
var averageRating = watchList.reduce(function (obj) {
if (obj.Director === "Christopher Nolan") {
count++;
sum = sum + parseFloat(obj.imdbRating);
}
return sum;
}, 0) / count;
// Add your code above this line
return averageRating;
}
The result is NaN, what I am doing wrong? I must use the arrow function, because standard function declaration produced unexpected results?
Thanks for help
I will give you hint.
const res = watchList.filter((d) => d.Director === 'James Cameron').map(x => x.averageRating));
Then another map to Numbers
res.map(Number)
Now use reduce to calculate average of numbers. Everything is explained here.
you can try:
const relevant = watchList.filter(movie => movie.Director === "Christopher Nolan");
const total = relevant.reduce((sum, movie) => sum + Number(movie.imdbRating), 0);
const average = total / relevant.length;
or combine the last 2 lines:
const relevant = watchList.filter(movie => movie.Director === "Christopher Nolan");
const average = relevant.reduce((sum, movie) => sum + Number(movie.imdbRating), 0) / relevant.length;
function getRating(watchList){
// Add your code below this line
var titles = watchList.filter(function(obj){
return obj.Director === "Christopher Nolan";
});
//message(titles);
var averageRating = titles
.reduce( function(sum,obj){
return sum = sum + parseFloat(obj.imdbRating);
}, 0)/titles.length;
//message(watchList.Director);
// Add your code above this line
return averageRating;
}
let averageRating = watchList
.filter(movie => movie.Director === "Christopher Nolan")
.map(movie => Number(movie.imdbRating))
.reduce((sum, movie, index, arr) => ((movie/arr.length)+ sum), 0);
Related
I have an array of four numbers, something like [597103978, 564784412, 590236070, 170889704] and I need to make sure that the variance is no more than 10%, for example for the array above, the check must fail because of the number 170889704.
Can someone suggest me a good method how to do that is Javascript?
Thanks in advance!
I would do it using Array.every
const arr = [597103978, 564784412, 590236070, 170889704];
const variance = (n, m) => {
return Math.abs( (n - m) / n );
};
const isLessThanTenPercent = (n) => {
return ( n < 0.1 );
};
const arrayIsGood = arr.every((n, i) => {
// m is the next element after n
const m = arr[i+1];
if (Number.isInteger(m)) {
const v = variance(n, m);
return isLessThanTenPercent(v);
} else {
// if m is not an integer, we're at the last element
return true;
}
});
console.log({arrayIsGood});
How do I filter the data in collection in Firestore
If the first letter is "+" then I want to get filtered in Income section if the first letter is "-" then I want to get filtered in Expenditure Section
I tried this, but not working:
const getUsers = async()=>{
total_income_amount = await db.collection("users").get().then((querySnapshot) => {
const sum = querySnapshot.docs.filter((item) => item > 0).reduce((a, b) => a + b.data().amount, 0)
return sum
})
}
I am getting the output as 0
and I want the output with two decimal places
EDIT
Here's my code:
total_amount = db.collection("users").get().then((querySnapshot) => {
var total_sum = 0;
var income_sum = 0;
var exp_sum = 0;
querySnapshot.docs.forEach(doc => {
const amount = doc.data().amount;
amount >= 0.0? income_sum += amount : exp_sum -= amount;
total_sum += amount;
});
return {total: total_sum, income: income_sum, expense: exp_sum }
}).finally(result => console.log("Total: ", result));
You can loop through the list of values and append the values once rather than looping through it 5 times with a reduce & filter
total_amount = db.collection("users").get().then((querySnapshot) => {
var total_sum = 0;
var income_sum = 0;
var exp_sum = 0;
querySnapshot.docs.forEach(doc => {
const amount = doc.data().amount;
amount >= 0.0? income_sum += amount : exp_sum -= amount;
total_sum += amount;
});
return {total: total_sum, income: income_sum, expense: exp_sum }
})
.finally(result => console.log("TOTALS", result);
EDIT
It's not good to make major changes to your Question
but in general, you can truncate all number's to a decimal place using toFixed() on the final output
https://www.w3schools.com/jsref/jsref_tofixed.asp
UPDATE
Ensure your numbers are converted to real numbers from user inputs with Number(value) if the typeof returned is not a number, you can know if it is valid or not.
Once this has been done, ensure you return the correct calls as needed as scripts also only fire once.
when rendering values inside HTML, you want to use an embedded <span> tag with the appropriate id tag rather than editing it via javascript
I want to give the user a prize when he signs in;
but it needs to be there some rare prizes so I want to appear prizes with different chances to appear using percents
i want to display one of these
[50 : 'flower'], [30 : 'book'], [20 : 'mobile'];
using percents they have
if there any way using Node.js or just javascript functions it would be great
You can create a function to get weighted random results, something like this:
const weightedSample = (items) => {
// cache if necessary; in Chrome, seems to make little difference
const total = Object.values(items).reduce((sum, weight) => sum + weight, 0)
const rnd = Math.random() * total
let accumulator = 0
for (const [item, weight] of Object.entries(items)) {
accumulator += weight
if (rnd < accumulator) {
return item
}
}
}
// check frequencies of each result
const prizes = { flower: 50, book: 30, mobile: 20 }
const results = Object.fromEntries(Object.keys(prizes).map(k => [k, 0]))
for (let i = 0; i < 1e6; ++i) {
const prize = weightedSample(prizes)
++results[prize]
}
// sample results: { flower: 500287, book: 299478, mobile: 200235 }
console.log(results)
This will work regardless of whether the weights add up to 100, whether they're integers, and so on.
'Right off the top of my head'-approach would be to prepare an array where each source item occurs the number of times that corresponds to respective probability and pick random item out of that array (assuming probability value has no more than 2 decimal places):
// main function
const getPseudoRandom = items => {
const {min, random} = Math,
commonMultiplier = 100,
itemBox = []
for(item in items){
for(let i = 0; i < items[item]*commonMultiplier; i++){
const randomPosition = 0|random()*itemBox.length
itemBox.splice(randomPosition, 0, item)
}
}
return itemBox[0|random()*itemBox.length]
}
// test of random outcomes distribution
const outcomes = Array(1000)
.fill()
.map(_ => getPseudoRandom({'flower': 0.5, 'book': 0.3, 'mobile': 0.2})),
distribution = outcomes.reduce((acc, item, _, s) =>
(acc[item] = (acc[item]||0)+100/s.length, acc), {})
console.log(distribution)
.as-console-wrapper{min-height:100%;}
While above approach may seem easy to comprehend and deploy, you may consider another one - build up the sort of probability ranges of respective width and have your random value falling into one of those - the wider the range, the greater probability:
const items = {'flower': 0.5, 'book': 0.2, 'mobile': 0.2, '1mUSD': 0.1},
// main function
getPseudoRandom = items => {
let totalWeight = 0,
ranges = [],
rnd = Math.random()
for(const itemName in items){
ranges.push({
itemName,
max: totalWeight += items[itemName]
})
}
return ranges
.find(({max}) => max > rnd*totalWeight)
.itemName
},
// test of random outcomes distribution
outcomes = Array(1000)
.fill()
.map(_ => getPseudoRandom(items)),
distribution = outcomes.reduce((acc, item, _, s) =>
(acc[item] = (acc[item]||0)+100/s.length, acc), {})
console.log(distribution)
"Certain probability" and "random" could lead to different approaches!
If you want random each time, something like:
let chances = [[0.2,'mobile'],[0.5,'book'],[1.0,'flower']]
let val = Math.random() // floating number from 0 to 1.0
let result = chances.find( c => c[0] <= val )[1]
This will give a random result each time. It could be possible to get 'mobile' 100 times in a row! Rare, of course, but a good random number generate will let that happen.
But perhaps you want to ensure that, in 100 results, you only hand out 20 mobiles, 30 books, and 50 flowers. Then you might want a "random array" for each user. Pre-fill the all the slots and remove them as they are used. Something like:
// when setting up a new user
let userArray = []
let chances = [[20,'mobile'],[30,'book'],[50,'flower']]
changes.forEach( c => {
for(let i = 0; i < c[0]; i++) userArray.push(c[1])
})
// save userArray, which has exactly 100 values
// then, when picking a random value for a user, find an index in the current length
let index = Math.floor(Math.random() * userArray.length)
let result = userArray[index]
userArray.splice(index,1) // modify and save userArray for next login
if(userArray.length === 0) reinitializeUserArray()
There are different approaches to this, but just some ideas to get you started.
I have function taken from this example here that works well, except does not address any zeros that may be in the number, so everything is equaling zero when executing the function.
Multiplying individual digits in a number with each other in JavaScript
function digitsMultip(data) {
let arr = [];
for (let i of data) {
if (data[i] === 0) {
arr.push(data[i]);
}
}
return [...data.toString()].reduce((p, v) => p * v);
};
console.log(digitsMultip(3025));
I added to it a for-loop that accounts for the zero and remove it, but im doing something wrong here.
Uncaught TypeError: data is not iterable
DESIRED OUTPUT
3025 => 3 * 2 * 5 = 30
This iterates over the characters in your number. If the character is not "0" then it is added to the array. This array is then reduced by multiplying the values and then returned.
function digitsMultip(data) {
const arr = [];
for(let number of String(data)) {
if (number !== "0")
arr.push(number);
}
return arr.reduce((p, v) => p * v);
};
console.log(digitsMultip(3025));
You are getting that error because you are trying to iterate over a number.
Passing in a string or converting the number to string before iterating it would make it work.
Instead of looping it that way, a better and readable way would be to use the filter method to filter out the chars before multiplying:
function digitsMultip(data) {
return [...data.toString()].filter(n => n > '0').reduce((p, v) => p * v);
};
console.log(digitsMultip(3025));
Turn the input into a string, then split, filter the zeros and reduce multiplying
const input = 1203
const removeZeros = number =>{
const arr = number.toString().split('').filter(i => i !== '0')
return arr.reduce((a,c) => parseInt(a) * parseInt(c))
}
console.log(removeZeros(input))
One line version
const removeZeros = n => [...n.toString()].filter(c => c !== '0').map(x => parseInt(x)).reduce((a,c) => a*c)
Ive been reading everything online but its not exactly what I need
var x = 'a1b2c3d4e5'
I need something to get me to
using 1 the answer should be abcde
using 2 the answer should be 12345
using 3 the answer should be b3e
the idea behind it if using 1 it grabs 1 skips 1
the idea behind it if using 2 it grabs 2 skips 2
the idea behind it if using 3 it grabs 3 skips 3
I dont want to use a for loop as it is way to long especially when your x is longer than 300000 chars.
is there a regex I can use or a function that Im not aware of?
update
I'm trying to some how implement your answers but when I use 1 that's when I face the problem. I did mention trying to stay away from for-loops the reason is resources on the server. The more clients connect the slower everything becomes. So far array.filter seem a lot quicker.
As soon as I've found it I'll accept the answer.
As others point out, it's not like regular expressions are magic; there would still be an underlying looping mechanism. Don't worry though, when it comes to loops, 300,000 is nothing -
console.time('while')
let x = 0
while (x++ < 300000)
x += 1
console.timeEnd('while')
// while: 5.135 ms
console.log(x)
// 300000
Make a big string, who cares? 300,000 is nothing -
// 10 chars repeated 30,000 times
const s =
'abcdefghij'.repeat(30000)
console.time('while string')
let x = 0
let interval = 2
let values = []
while (x < s.length)
{ values.push(s[x])
x += interval
}
let result = values.join('')
console.timeEnd('while string')
// while string: 31.990ms
console.log(result)
console.log(result.length)
// acegiacegiacegiacegiacegiacegiacegiacegia...
// 150000
Or use an interval of 3 -
const s =
'abcdefghij'.repeat(30000)
console.time('while string')
let x = 0
let interval = 3
let values = []
while (x < s.length)
{ values.push(s[x])
x += interval
}
let result = values.join('')
console.timeEnd('while string')
// while string: 25.055ms
console.log(result)
console.log(result.length)
// adgjcfibehadgjcfibehadgjcfibehadgjcfibe...
// 100000
Using a larger interval obviously results in fewer loops, so the total execution time is lower. The resulting string is shorter too.
const s =
'abcdefghij'.repeat(30000)
console.time('while string')
let x = 0
let interval = 25 // big interval
let values = []
while (x < s.length)
{ values.push(s[x])
x += interval
}
let result = values.join('')
console.timeEnd('while string')
// while string: 6.130
console.log(result)
console.log(result.length)
// afafafafafafafafafafafafafafafafafafafafafafa...
// 12000
You can achieve functional style and stack-safe speed simultaneously -
const { loop, recur } = require('./lib')
const everyNth = (s, n) =>
loop
( (acc = '', x = 0) =>
x >= s.length
? acc
: recur(acc + s[x], x + n)
)
const s = 'abcdefghij'.repeat(30000)
console.time('loop/recur')
const result = everyNth(s, 2)
console.timeEnd('loop/recur')
// loop/recur: 31.615 ms
console.log(result)
console.log(result.length)
// acegiacegiacegiacegiacegiacegiacegia ...
// 150000
The two are easily implemented -
const recur = (...values) =>
({ recur, values })
const loop = f =>
{ let acc = f()
while (acc && acc.recur === recur)
acc = f(...acc.values)
return acc
}
// ...
module.exports =
{ loop, recur, ... }
And unlike the [...str].filter(...) solutions which will always iterate through every element, our custom loop is much more flexible and receives speed benefit when a higher interval n is used -
console.time('loop/recur')
const result = everyNth(s, 25)
console.timeEnd('loop/recur')
// loop/recur: 5.770ms
console.log(result)
console.log(result.length)
// afafafafafafafafafafafafafafa...
// 12000
const recur = (...values) =>
({ recur, values })
const loop = f =>
{ let acc = f()
while (acc && acc.recur === recur)
acc = f(...acc.values)
return acc
}
const everyNth = (s, n) =>
loop
( (acc = '', x = 0) =>
x >= s.length
? acc
: recur(acc + s[x], x + n)
)
const s = 'abcdefghij'.repeat(30000)
console.time('loop/recur')
const result = everyNth(s, 2)
console.timeEnd('loop/recur')
// loop/recur: 31.615 ms
console.log(result)
console.log(result.length)
// acegiacegiacegiacegiacegiacegiacegia ...
// 150000
Since I'm not an expert of regex, I'd use some fancy es6 functions to filter your chars.
var x = 'a1b2c3d4e5'
var n = 2;
var result = [...x].filter((char, index) => index % n == 0);
console.log(result);
Note that because 0 % 2 will also return 0, this will always return the first char. You can filter the first char by adding another simple check.
var result = [...x].filter((char, index) => index > 0 && index % n == 0);
As a variant:
function getNth(str, nth) {
return [...str].filter((_, i) => (i + 1) % nth === 0).join('');
}
console.log(getNth('a1b2c3d4e5', 2)); // 12345
console.log(getNth('a1b2c3d4e5', 3)); // b3e
What I'd suggest, to avoid having to iterate over the entire array, is to step straight into the known nth's.
Here's a couple of flavors:
function nthCharSubstr(str, nth) {
let res = "";
for (let i = nth - 1; i < str.length; i += nth) {
res += string[i];
}
return res;
}
More ES6-y:
const nthCharSubstr = (str, nth) =>
[...Array(parseInt(str.length / nth)).keys()] // find out the resulting number of characters and create and array with the exact length
.map(i => nth + i * nth - 1) // each item in the array now represents the resulting character's index
.reduce((res, i) => res + str[i], ""); // pull out each exact character and group them in a final string
This solution considers this comment as being valid.