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How to generate 3 names without the same name repeated [duplicate]

This question already has an answer here:
Math random to find Names in an Array while not duplicating
(1 answer)
Closed 1 year ago.
window.onload = start;
function start () {
var name = ["Hans","Ole","Nils","Olav","Per","Knut","Kari","Line","Pia"]
var random = Math.floor(Math.random()*8)
var random2 = Math.floor(Math.random()*8)
var random3 = Math.floor(Math.random()*8)
var name2 = []
name2.push(name[random])
name2.push(name[random2])
name2.push(name[random3])
for(i=0; i<3; i++) {
document.getElementById("par").innerHTML += name2[i] + "<br/>" ;
}
}
So far with this code i can generate 3 random names from the name array. But i want the 3 names not to be repeated, and I don't know how to make that happen.

Perhaps this could help. I randomized the order of the array and then just pick the first three elements. This allows for zero repeats of names and generating a new answer each time the function is ran. Not sure what your HTML looks like so I just added the id "demo".
var players = ["Hans","Ole","Nils","Olav","Per","Knut","Kari","Line","Pia"];
function tournament() {
var names = [];
players.sort(function(a,b){return 0.5 - Math.random()});
for (i=0; i<3; i++){
names.push(players[i]);
}
document.getElementById("demo").innerHTML = names;
}

I created a solution that uses recursion.
The function randomNames gets repeated three times. Each time it gets called count gets increased and names is an array without the names that are already taken. It returns an array that holds the three random names.
function start () {
var name = ["Hans","Ole","Nils","Olav","Per","Knut","Kari","Line","Pia"]
function randomNames(count, names) {
if(count >= 3) return [];
var random = Math.floor(Math.random()*(names.length-1));
// remove current name
var name = names.splice(random, 1);
return randomNames(++count, names).concat(name);
}
var random = randomNames(0, name);
}

You could use a hash table for the chosen items and check against until all wanted items are found.
window.onload = start;
function start() {
var name = ["Hans", "Ole", "Nils", "Olav", "Per", "Knut", "Kari", "Line", "Pia"],
hash = {},
random;
while (Object.keys(hash).length < 3) {
do {
random = Math.floor(Math.random() * name.length);
} while (hash[random])
hash[random] = true;
document.getElementById("par").innerHTML += name[random] + "<br/>";
}
}
<div id="par"></div>
ES6 with Set
window.onload = start;
function start() {
var name = ["Hans", "Ole", "Nils", "Olav", "Per", "Knut", "Kari", "Line", "Pia"],
hash = new Set,
random;
while (hash.size < 3) {
do {
random = Math.floor(Math.random() * name.length);
} while (hash.has(random))
hash.add(random);
document.getElementById("par").innerHTML += name[random] + "<br/>";
}
}
<div id="par"></div>

Having Issue On Generating Random Numbers More Than Random Rage Number

I need to generate 30 Random Numbers between 1 to 20. I am using this code but this is making conflict since the loop number is bigger than the Random range (I guess!)
var arr1 = [];
for (var i = 0; i < 30;) {
var ran = Math.floor(Math.random() * 20) + 1;
if ( arr1.indexOf(ran) == -1)
arr1[i++] = ran;
}
can you please let me know why this is happening and how I can prevent this to create 30 random numbers?
Thanks

I created a fiddle here , have a look
https://jsbin.com/kagixi/edit?html,js,output
In first case, we are updating values by iterating over all the indices.
var list = new Array(30).fill(0);
list.forEach(function(d, index){
list[index] = Math.floor(Math.random() * 20) + 1;
});
console.log(list);
Another way of doing this is to initialize array just to loop and then simply create a new array with same length or replace the existing one as I did in this example.
var list2 = new Array(30).fill(0);
list2 = list2.map(function(){
return Math.floor(Math.random() * 20) + 1;
});

You miss the third argument on your for statement.
Try this:
var arr1 = [];
for (var i = 0; i < 30; i++) {
arr1[i] = Math.floor(Math.random() * 20) + 1;
}

Your code creates an infinite loop.
Your random numbers are between 1 and 20 but you want 30 of them in your array. The check for duplicates in the line if ( arr1.indexOf(ran) == -1) is guaranteed to return false after 20 iterations, creating an infinite loop.

Javascript syntax issue in code

Can someone tell me why this bit of JavaScript is buggy?
I have HTML also, but I don't want to make this a massive code dump.
<script type = 'text/javascript'>
var playerCards = [];
var dealerCards = [];
function deal() {
var newCard = Math.random() % 12;
var newCard2 = Math.random() % 12;
playerCards += newCard;
playerCards += newCard2;
var counter = 0;
for (var i = 0; i < playerCards.length; ++i) {
counter += i;
}
document.getElementById("playerTotal").innerHTML = counter;
var dCounter = 0;
for (var j = 0; j < playerCards.length; ++j) {
dCounter += j;
}
document.getElementById("dealerTotal").innerHTML = dCounter;
}
</script>
I'm gonna assume this is a silly syntax error someplace, but I can't find it.

I'm guessing that this isn't doing what you expect it to:
playerCards += newCard;
playerCards += newCard2;
Try this instead:
playerCards.push(newCard);
playerCards.push(newCard2);
The first snippet is trying to "add" a number to an array, which doesn't exactly make sense. Through some arcane JavaScript rules, this turns the result into a string.
I'm guessing that you want to concatenate to an array instead.

Math.random returns a number between 0 and 1 - so Math.random() % 12 will probably be zero
var playerCards = [];
playerCards += newCard; //
what are you even trying to do there?
var counter = 0;
for (var i = 0; i < playerCards.length; ++i) {
counter += i;
}
if playerCards had a length, this loop would result in counter having value of 0, 1, 3, 6, 10 .. n(n+1) / 2 - probably not what you intended, but who knows

Javascript: using a for statement as a variable

I'm fairly new to javascript and something I've been playing with lately is the 'for' statement. I'm questioning one thing, though. I've learned how to make a 'for' statement do things as if it was an output, like this:
for (i = 0; i < 3; i++) {
console.log(i);
}
But what if you want to set a variable for the whole output of the 'for' statement?
var destinationArray = ["town", "areas", "bosses"];
var destinationArraySet = 1;
var i;
for ( i = 0; i < destinationArraySet; i++) {
console.log(destinationArray[i]);
} /*the whole thing should be equal to var destination */
var userDestinationPrompt = ("Where would you like to go? Available places: " +
/* var destination */
+
".").toUpperCase();
To give some more context: I'm making a game that allows further destinations when the destination before is cleared. Once that's achieved, I set destinationArraySet to a higher value, which means that more places would be logged and put after 'Available places'.
Help would be very appreciated! If there's something not clear enough let me know.

The for statement is not an expression, so it doesn't have a return value. Use a variable to collect values in the loop:
var destination = '';
for (var i = 0; i < destinationArraySet; i++) {
destination += destinationArray[i] + ' ';
}
Of course, if you only want to concatenate the values in part of an array, you can use the slice method to get part of it, then the join method:
var destination = destinationArray.slice(0, destinationArraySet).join(' ');

var destination = '';
var destinationArray = ["town", "areas", "bosses"];
var destinationArraySet = 1;
for (var i = 0; i < destinationArraySet; i++) {
destination += destinationArray[i] + '\n';
}
console.log(destination);

Try this -
var destinationArray = ["town", "areas", "bosses"];
var destinationArraySet = 1;
var i;
var availablePlaces = '';
var separator = '';
for ( i = 0; i < destinationArraySet; i++) {
availablePlaces += separator + destinationArray[i];
separator = ', ';
}
var userDestinationPrompt = ("Where would you like to go? Available places: " +
availablePlaces + ".").toUpperCase();

The for statement doesn't have an "output", it's not a function. Thinking for as a function will give you troubles later on. for is simply a statement that continuously execute the block of code inside. It does not "output", or in other words, return any value.
Do this instead:
var destinationArray = ["town", "areas", "bosses"], destinationArraySet = 1;
var userDestinationPrompt = ("Where would you like to go? Available places: " +
destinationArray.slice(0, destinationArraySet).join("\n")
+ ".").toUpperCase();
prompt(userDestinationPrompt);
Demo: http://jsfiddle.net/7c2b9q7m/1/
destinationArray.slice(0, destinationArraySet): Cuts the array to the specified length.
.join("\n"): Join the newly created array by \ns (newline) to micic the default console.log behavior.

Javascript generate random unique number every time

Ok so i need to create four randomly generated numbers between 1-10 and they cannot be the same. so my thought is to add each number to an array but how can I check to see if the number is in the array, and if it is, re-generate the number and if it isnt add the new number to the array?
so basically it will go,
1.create new number and add to array
2.create second new number, check to see if it exist already, if it doesn't exist, add to array. If it does exist, re-create new number, check again etc...
3.same as above and so on.

You want what is called a 'random grab bag'. Consider you have a 'bag' of numbers, each number is only represented once in this bag. You take the numbers out, at random, for as many as you need.
The problem with some of the other solutions presented here is that they randomly generate the number, and check to see if it was already used. This will take longer and longer to complete (theoretically up to an infinite amount of time) because you are waiting for the random() function to return a value you don't already have (and it doesn't have to do that, it could give you 1-9 forever, but never return 10).
There are a lot of ways to implement a grab-bag type solution, each with varying degrees of cost (though, if done correctly, won't ever be infinite).
The most basic solution to your problem would be the following:
var grabBag = [1,2,3,4,5,6,7,8,9,10];
// randomize order of elements with a sort function that randomly returns -1/0/1
grabBag.sort(function(xx,yy){ return Math.floor(Math.random() * 3) - 1; })
function getNextRandom(){
return grabBag.shift();
};
var originalLength = grabBag.length;
for(var i = 0; i < originalLength; i++){
console.log(getNextRandom());
}
This is of course destructive to the original grabBag array. And I'm not sure how 'truly random' that sort is, but for many applications it could be 'good enough'.
An slightly different approach would be to store all the unused elements in an array, randomly select an index, and then remove the element at that index. The cost here is how frequently you are creating/destroying arrays each time you remove an element.

Here are a couple versions using Matt's grabBag technique:
function getRandoms(numPicks) {
var nums = [1,2,3,4,5,6,7,8,9,10];
var selections = [];
// randomly pick one from the array
for (var i = 0; i < numPicks; i++) {
var index = Math.floor(Math.random() * nums.length);
selections.push(nums[index]);
nums.splice(index, 1);
}
return(selections);
}
You can see it work here: http://jsfiddle.net/jfriend00/b3MF3/.
And, here's a version that lets you pass in the range you want to cover:
function getRandoms(numPicks, low, high) {
var len = high - low + 1;
var nums = new Array(len);
var selections = [], i;
// initialize the array
for (i = 0; i < len; i++) {
nums[i] = i + low;
}
// randomly pick one from the array
for (var i = 0; i < numPicks; i++) {
var index = Math.floor(Math.random() * nums.length);
selections.push(nums[index]);
nums.splice(index, 1);
}
return(selections);
}
And a fiddle for that one: http://jsfiddle.net/jfriend00/UXnGB/

Use an array to see if the number has already been generated.
var randomArr = [], trackingArr = [],
targetCount = 4, currentCount = 0,
min = 1, max = 10,
rnd;
while (currentCount < targetCount) {
rnd = Math.floor(Math.random() * (max - min + 1)) + min;
if (!trackingArr[rnd]) {
trackingArr[rnd] = rnd;
randomArr[currentCount] = rnd;
currentCount += 1;
}
}
alert(randomArr); // Will contain four unique, random numbers between 1 and 10.
Working example: http://jsfiddle.net/FishBasketGordo/J4Ly7/

var a = [];
for (var i = 0; i < 5; i++) {
var r = Math.floor(Math.random()*10) + 1;
if(!(r in a))
a.push(r);
else
i--;
}
That'll do it for you. But be careful. If you make the number of random numbers generated greater than the may number (10) you'll hit an infinite loop.

I'm using a recursive function. The test function pick 6 unique value between 1 and 9.
//test(1, 9, 6);
function test(min, max, nbValue){
var result = recursValue(min, max, nbValue, []);
alert(result);
}
function recursValue(min, max, nbValue, result){
var randomNum = Math.random() * (max-min);
randomNum = Math.round(randomNum) + min;
if(!in_array(randomNum, result)){
result.push(randomNum);
nbValue--;
}
if(nbValue>0){
recursValue(min, max, nbValue, result);
}
return result;
}
function in_array(value, my_array){
for(var i=0;i< my_array.length; i++){
if(my_array[i] == value){
console.log(my_array+" val "+value);
return true;
}
}
return false;
}

Here is a recursive function what are you looking for.
"howMany" parameter is count of how many unique numbers you want to generate.
"randomize" parameter is biggest number that function can generate.
for example : rand(4,8) function returns an array that has 4 number in it, and the numbers are between 0 and 7 ( because as you know, Math.random() function generates numbers starting from zero to [given number - 1])
var array = [];
var isMatch= false;
function rand(howMany, randomize){
if( array.length < howMany){
var r = Math.floor( Math.random() * randomize );
for( var i = 0; i < howMany; i++ ){
if( array[i] !== r ){
isMatch= false;
continue;
} else {
isMatch= true;
break;
}
}
if( isMatch == false ){
array.push(r);
ran(howMany, randomize);
}
ran(howMany, randomize);
return array;
}
}

In your answer earlier, you do have a small bug. Instead of
var originalLength = grabBag.length;
for(var i = 0; i < originalLength .length; i++){
console.log(getNextRandom());
}
I believe you meant:
var originalLength = grabBag.length;
for(var i = 0; i < originalLength; i++){
console.log(getNextRandom());
}
Thanks.