Develop Reference

Javascript adding multiple arrays in a loop

I am trying to add multiple arrays in javascript.
Here are my arrays I have made, and are working.
function getAmountSpent(){
var amountSpent = ((Math.random() * 500) + 1);
return amountSpent.toFixed(2)
}
function getGift(){
var gift = ((Math.random()* 50) + 1);
return gift.toFixed(2)
}
var names = ["Jeremy","Arun","Alisa","Rohan","Dana"];
var spent = [];
for (let i = 0; i < 5; i++) {
spent.push(getAmountSpent());
}
var gifts = [];
for (let i = 0; i<5; i++) {
gifts.push(getGift());
}
What I need help with is adding these arrays in a new function. I have began writing the code, and I am not sure what is wrong.
var totals =[];
for (let i=0; i<5; i++) {
totals.push(getSumTotals())
}
function getSumTotals(a){
totals= spent+(spent * gifts);
return totals.toFixed(2)
}
From what you can see, I am trying to add up the totals much like this:
totals[0] = spent[0] + (spent[0] * gifts[0]);
totals[1] = spent[1] + (spent[1] * gifts[1]);
totals[2] = spent[2] + (spent[2] * gifts[2]);
totals[3] = spent[3] + (spent[3] * gifts[3]);
totals[4] = spent[4] + (spent[4] * gifts[4]);
if it helps, the professor added guided instructions for function getSumTotals(a) stating:
This function will return the sum of the elements in array a.
You will be passing the array that holds your totals to
the parameter a. Be sure to treat the values in a as numbers.
I am not sure if this helps but here is the output to my document.
Current Total should equal (spent) + (spent * gifts). For instance, for Jeremy in this example, current total should equal:
$36.55 + ($36.55*0.0626) = $38.83. Since there are many variables involved, I am not 100% sure what I should write for function getSumTotals(a)
The parameter "a" is a placeholder because I am not sure how many parameter values I need, and the proper format I need to use.

As for the code...
You're both
not passing an index to getSumTotals
not using this parameter within getSumTotals to access your spent and gifts arrays
var totals =[];
for (let i=0; i<5; i++) {
totals.push(getSumTotals(i)) // you were missing i
}
function getSumTotals(idx) { // I took liberties to rename this
totals = spent[idx] + (spent[idx] * gifts[idx]);
return totals.toFixed(2);
}
Now for the Math...
All that said, this math of spent[i] + spent[i] * gifts[i] doesn't make much sense either. Was this specified in the problem?

you may use like this
defined gifts
gifts=[45,43,32];
defined spends
spends=[43,32,21];
this is the getSumTotal funtion
getSumTotal=(x)=>(x.a+x.b)
this is where added
totals=gifts.map((d1,i)=>{
return fu({a:gifts[i],b:spends[i]})
})

I understand this is your assignment, however - if the idea is to both generate arrays, and then add them together, it is a redundant step. Just use the name array to iterate once and do all your calculations within that single loop.
Here, I had some fun and took some liberties, but hopefully you see why multiple arrays are redundant.
function getSumTotals() {
const getAmountSpent = () => Math.random() * 500 + 1;
const getGift = () => Math.random() * 50 + 1;
const names = ["Jeremy", "Arun", "Alisa", "Rohan", "Dana"];
let totals = []
names.forEach((name, i) => {
let spent = getAmountSpent()
let gifts = getGift()
let $$$ = (spent + spent * gifts).toFixed(2);
totals[i] = $$$
console.log(`${name} cost me $${$$$}${'!'.repeat(($$$/1000) | 1)}`)
});
return totals;
}
getSumTotals()

Note, that toString returns a type of "String", but not "Number".
When you try to sum a number with string, you get a concatenated string "1" + 2 = "12"
To turn a string into Number, you must use a Number("str") function, or just a bunary + before the string:
console.log( "1" + 2 );
console.log( Number("1") + 2 );
console.log( +"1" + 2 );
Also, you use the same loop 3 times, but can use just one loop instead, and call all functions inside the one loop. And use your array.length instead of fixed number 5:
let names = ["Jeremy", "Arun", "Alisa", "Rohan", "Dana"];
let spent = [];
let gifts = [];
let totals = [];
for (let i = 0; i < names.length; i++) {
spent.push( getAmountSpent() );
gifts.push( getGift() );
totals.push( getSumTotals(i) );
}
console.log( totals );
function getAmountSpent() {
return rand(1, 500, 2);
}
function getGift() {
return rand(1, 50, 2);
}
function getSumTotals(i) {
return +( spent[i] * ( 1 + gifts[i] ) ).toFixed(2);
}
function rand(from, to, fixed = 0){
return +(Math.random()*( to - from ) + from).toFixed(fixed);
}
P.s. Math.random() returns a number between 0 (included) and 1 (not included). If you need a random number between (example) 20 and 100, Math.random()*(100-20) will give a number between 0 and 80. After adding +20 to the result, you get a number from 20 to 100. That's what does this formula Math.random()*( to - from ) + from
P.P.s. Another way, to get the same thing:
var names = ["Jeremy", "Arun", "Alisa", "Rohan", "Dana"].reduce( (prev, elem) => {
let spent = rand(1, 500, 2);
let gift = rand(1, 50, 2);
prev[elem] = new UserData( spent, gift );
return prev;
}, {});
console.log( "Jeremy spent: " + names.Jeremy.spent );
console.log( names );
function rand(from, to, fixed = 0){
return +(Math.random()*( to - from ) + from).toFixed(fixed);
}
function UserData(spent, gift){
this.spent = spent;
this.gift = gift;
this.total = +(spent * ( 1 + gift )).toFixed(2);
}
/* Google → Array reduce, Constructor functions */

function getAmountSpent(){
let amountSpent = ((Math.random() * 500) + 1);
return Number(amountSpent.toFixed(2))
}
function getGift(){
let gift = ((Math.random()* 50) + 1);
return Number(gift.toFixed(2))
}
let names = ["Jeremy","Arun","Alisa","Rohan","Dana"];
let spent = [];
let gifts = [];
let totals =[];
for (let i = 0; i < names.length; i++) {
spent.push(getAmountSpent());
gifts.push(getGift());
totals[i] = (spent[i]+(spent[i] * gifts[i])).toFixed(2);
totals[i] = parseFloat(totals[i])
}
Hi there
I don't think you need a function to add the totals. you just need to loop through and assign totals[i] to spent[i] + (spent[i] * gifts[i]).
then you can use the parseFloat and toFixed function to change the string to a number. remember toFixed() function turns numbers to string. so you need to use the parseFloat to change it to number again as shown in the code above. or you can come up with an easy way of changing it to number. I hope this helps!

Getting new colors randomly with loop

I am trying to randomize colors by generating random number, then applying
it to array to get an color array containing font-color and background-color.
At every "skill" I want to have unique color scheme. So each time I loop skill array I loop color array to fetch color scheme. If this color scheme number (which is same as the randomNumber) is already in use I random again. I do this with do/while loop. When color is not found it pushes it to usedColors array and paints the picture.
For some reason I am still getting same colors. I pasted two pictures to the bottom. Console.log image is about usedColors array (the randomly generated numbers)
var usedColors = [];
$.each(knowledges, (i, knowledge) => {
do {
var r = Math.floor(Math.random() * Math.floor(colors.length)),
rColors = colors[r];
} while ($.inArray(r, usedColors) == 0);
usedColors.push(r);
$("#knowledges div").append(
$("<p />").addClass("knowledge").text(knowledge).css({"background-color": rColors[0], "color": rColors[1]})
);
});

inArray gives position of the matching element. So compare against -1, to know that element is not present in the usedColors array.
var usedColors = [];
$.each(knowledges, (i, knowledge) => {
do {
var r = Math.floor(Math.random() * Math.floor(colors.length)),
rColors = colors[r];
} while ($.inArray(r, usedColors) != -1);
usedColors.push(r);
$("#knowledges div").append(
$("<p />").addClass("knowledge").text(knowledge).css({"background-color": rColors[0], "color": rColors[1]})
);
});

To generate array of unique numbers from certain interval you can do this.
In your case the range will be 0, arr.length - 1.
// function that will generate random unique random numbers between start
// and end, and store already generated numbers in closure
function generateUniqueRandom(start, end) {
const used = [];
function generateInner() {
let r;
while (!r) {
r = Math.floor(Math.random() * (end - start) + 1) + start;
if (used.includes(r)) {
r = null;
} else {
used.push(r);
}
}
return r;
}
return generateInner;
}
const random1 = generateUniqueRandom(0, 20);
const nums1 = [];
for (let i = 0; i < 10; i++) {
nums1.push(random1());
}
console.log(nums1);
const random2 = generateUniqueRandom(0, 20);
const nums2 = [];
for (let i = 0; i < 20; i++) {
nums2.push(random2());
}
console.log(nums2);
But you need to be careful not to generate more numbers that the specified range is, otherwise you will be stuck in an infinite loop.

In your while loop, are you checking if the array is unique? If so, it looks like you may not be using $.inArray correctly.
Put this in your while loop:$.inArray(r, usedColors) !== -1
jQuery.inArray(), how to use it right?

I think your loop method has many interactions, I mean your loop is traveling so much that it only ends until you find the random number that is not in the array (A short performance problem). An alternative method so that the array elements are random:
function shuffleArray(a) {
for (let i = a.length - 1; i > 0; i--) {
const j = Math.floor(Math.random() * (i + 1));
[a[i], a[j]] = [a[j], a[i]];
}
return a;
}
const colors = [["black","green"], ["white","blue"], ["pink","white"]];
let usedColors = shuffleArray(colors);
//You can now do this:
$.each(knowledges, (i, knowledge) => {
$("#knowledges div").append(
$("<p />").addClass("knowledge").text(knowledge).css({"background-color": usedColors[i][0], "color": usedColors[i][1]})
);
});

return multiple numbers from the loop

I want to create a function that returns 50 random numbers out of 100. If I write console.log(getMines), it returns all fifty numbers. But if I want to actually use them, my loop returns only one number. What's the problem?
var getMines = function() {
for (count; count <= 100; count++) {
return "d" + (Math.floor(Math.random() * 50));
}
}

You can only return a single value from a function. So once you return your first number, the loop essentially ends.
Try this instead!
var getMines = function() {
var minesArray = [];
for (var count=0; count <= 100; count++) {
minesArray.push("d" + (Math.floor(Math.random() * 50)));
}
return minesArray;
}
This will return an array of all the numbers, which you can then iterate through to do what you need. You can sort the numbers, or sum them etc.
I feel I should point out that your code is returning 100 random numbers between 1 and 50, not 50 random numbers between 1 and 100. If thats what you want and you misspoke in the OP nbd, but if you want 50 random numbers between 1 and 100 change count to <= 50 and multiply Math.random() by 100 instead.

You need create a var and push randoms, like this
var getMines = function() {
var returnArray = [];
for (var count = 0; count <= 100; count++) {
returnArray.push("d" + (Math.floor(Math.random() * 50)));
}
return returnArray;
}

you can only return only once from a function, you can use an array or object, add all values to it and return it.
var getMines = function() {
var arr = [];
for (count; count <= 100; count++) {
arr.push("d" + (Math.floor(Math.random() * 50)));
}
return arr;
}

If I read you question right, you need 50 numbers with a random value out of 100.
You need to switch the numbers in the for loop and the factor for getting a random number and take a initial value of zero for the looping variable, as well as not return some value inside of the for loop.
var getMines = function() {
var count,
array = [];
for (count = 0; count < 50; count++) {
array.push("d" + (Math.floor(Math.random() * 100)));
}
return array;
}
console.log(getMines());
.as-console-wrapper { max-height: 100% !important; top: 0; }

That can also be done with some cool ES6 tricks:
const getMines = ()=> Array.from(
{length:50},
()=> "d" + Math.floor( Math.random() * 100 )
);

If you need any random 50 numbers between 1 and 100 (both inclusive, I have tweaked your version to following. See if that helps.
var getMines = function() {
var nums = [];
for (var count=1; count <= 50; count++) {
nums[count-1]=Math.floor(Math.random() * 100) + 1;
}
return nums;
}
console.log(getMines());

List array elements, one by one, with a click of a button

I am new to Javascript and working with the basics. I am wanting to create an array whose individual elements are randomly drawn, one at a time, with a click of a button, until all array elements are displayed on the screen. The code I have is almost there. But the issue is that when it runs, it always grabs 2 elements on the first button click, rather than 1. It runs well for the remaining elements. Sure would appreciate some insight to this problem. Thank you.
var myArray=['1','2','3','4','5','6','7']
var text = "";
var i;
function RandomDraw() {
for(i = 0; i < myArray.length; i+=text) {
var ri = Math.floor(Math.random() * myArray.length);
var rs = myArray.splice(ri, 1);
document.getElementById("showSplice").innerHTML = text+=rs;
//document.getElementById("showArrayList").innerHTML = myArray;
}
}

It "always" draws 2 elements because of the i+=text. Your array is small thus the loop needs 2 iteration (of cocatinating the strings to get the number i) to go over myArray.length.
First iteration:
i = 0 => 0 < myArray.length => true
prints number
Second iteration: (say '4' get choosen)
i = i + text and text = '4' => i = "04" => "04" < myArray.length => true
prints number
Third iteration: (say '3' get choosen)
i = i + text and text = '43' => i = "0443" => "0443" < myArray.length => false
loop breaks
So there is a possibility that two elements get printed. Depending on the length of the array, there could be more.
You don't need the loop, just choose a number and print it:
function RandomDraw() {
if(myArray.length > 0) { // if there still elements in the array
var ri = Math.floor(Math.random() * myArray.length); // do your job ...
var rs = myArray.splice(ri, 1);
document.getElementById("showSplice").textContent = rs; // .textContent is better
}
else {
// print a message indicating that the array is now empty
}
}

Another solution is to shuffle the array and then, on each click, pop the element from the shuffled array.
function shuffle(array) {
return array.sort(function() { return Math.random() - 0.5; });
}
var button = document.getElementById('button');
var origin = ['1','2','3','4','5','6','7'];
var myArray = shuffle(origin);
var currentValue = null;
button.onclick = function() {
currentValue = myArray.pop();
if(!!currentValue) {
console.log(currentValue);
}
}
<button id='button'>
get element
</button>
You can shuffle the array again on each click, but I think it is not necessary whatsoever...
If you're wondering about Math.random() - 0.5:
[...] Math.random is returning a number between 0 and 1. Therefore, if you call Math.random() - 0.5 there is a 50% chance you will get a negative number and 50% chance you'll get a positive number.
If you run a for loop and add these results in an array, you will effectively get a full distribution of negative and positive numbers.
https://teamtreehouse.com/community/mathrandom05

I would do it this way:
let myArray=['1','2','3','4','5','6','7']
function RandomDraw(){
const selectedIndex = Math.floor(Math.random() * myArray.length);
const selected = myArray[selectedIndex]
myArray = myArray.slice(0, selected).concat(myArray.slice(selected + 1));
return selected;
}
Every time you call RandomDraw it will return a random number, without repeating.

The way I understand it, you want to draw every items from the array after a single click. So the loop is needed.
As others have said, there are several issues in your for loop :
that i+= text makes no sense
you are looping until i reaches the length of your array, but you are splicing that array, hence reducing its length
You could correct your for loop :
function RandomDraw() {
var length = myArray.length;
var ri = 0;
for (var i=0;i<length;i++) {
ri = Math.floor(Math.random() * myArray.length);
console.log("Random index to be drawn : " + ri);
// removing that index from the array :
myArray.splice(ri, 1);
console.log("myArray after a random draw : ", myArray);
}
}
Or, you could use a while loop :
function RandomDraw() {
var ri = 0;
while (myArray.length > 0) {
ri = Math.floor(Math.random() * myArray.length);
console.log("Random index to be drawn : " + ri);
// removing that index from the array :
myArray.splice(ri, 1);
console.log("myArray after a random draw : ", myArray);
}
}

javascript - generate a new random number

I have a variable that has a number between 1-3.
I need to randomly generate a new number between 1-3 but it must not be the same as the last one.
It happens in a loop hundreds of times.
What is the most efficient way of doing this?

May the powers of modular arithmetic help you!!
This function does what you want using the modulo operator:
/**
* generate(1) will produce 2 or 3 with probablity .5
* generate(2) will produce 1 or 3 with probablity .5
* ... you get the idea.
*/
function generate(nb) {
rnd = Math.round(Math.random())
return 1 + (nb + rnd) % 3
}
if you want to avoid a function call, you can inline the code.

Here is a jsFiddle that solves your problem : http://jsfiddle.net/AsMWG/
I've created an array containing 1,2,3 and first I select any number and swap it with the last element. Then I only pick elements from position 0 and 1, and swap them with last element.

var x = 1; // or 2 or 3
// this generates a new x out of [1,2,3] which is != x
x = (Math.floor(2*Math.random())+x) % 3 + 1;

You can randomly generate numbers with the random number generator built in to javascript. You need to use Math.random().
If you're push()-ing into an array, you can always check if the previously inserted one is the same number, thus you regenerate the number. Here is an example:
var randomArr = [];
var count = 100;
var max = 3;
var min = 1;
while (randomArr.length < count) {
var r = Math.floor(Math.random() * (max - min) + min);
if (randomArr.length == 0) {
// start condition
randomArr.push(r);
} else if (randomArr[randomArr.length-1] !== r) {
// if the previous value is not the same
// then push that value into the array
randomArr.push(r);
}
}

As Widor commented generating such a number is equivalent to generating a number with probability 0.5. So you can try something like this (not tested):
var x; /* your starting number: 1,2 or 3 */
var y = Math.round(Math.random()); /* generates 0 or 1 */
var i = 0;
var res = i+1;
while (i < y) {
res = i+1;
i++;
if (i+1 == x) i++;
}

The code is tested and it does for what you are after.
var RandomNumber = {
lastSelected: 0,
generate: function() {
var random = Math.floor(Math.random()*3)+1;
if(random == this.lastSelected) {
generateNumber();
}
else {
this.lastSelected = random;
return random;
}
}
}
RandomNumber.generate();