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Javascript: Calculating Min/Max/Average

I wrote this code in my html site, in Javascript, but is not working right. Most times it seems to ignore some entries and just randomly selects which is the min/max value. Also, when I tried to calculate average values, I got a string instead of a number, even though the variable is declared as 0 in the beginning. e.g performing 0+1+1+2+3+5 = 011235 instead of 12.
Here is the code, thanks in advance.
**EDIT: I added the student average code in the end, but it doesn't work, it doesn't show any results on the page, not even the "student" + [i] part. On the other hand, the parseInt() command worked, and made everything work as it should, thank you :)
<script language = "javascript">
function myFunction() {
var course0 = [];
var course1 = [];
var course2 = [];
var minstugrade = 100;
var maxstugrade = 0;
var minstugradetext = "";
var maxstugradetext = "";
var stuavgarr = [];
var minstuavg = 100;
var maxstuavg = 0;
var minstuavgtext = "";
var maxstuavgtext = "";
var mincougrade = 100;
var maxcougrade = 0;
var mincougradetext = "";
var maxcougradetext = "";
var mincouavg = 100;
var maxcouavg = 0;
var mincouavgtext = "";
var maxcouavgtext = "";
var couavg = 0;
//add form items to array
var x = document.getElementById("course0");
var i;
for (i = 0; i < x.length ;i++) {
course0.push(parseInt(x.elements[i].value));
}
var x = document.getElementById("course1");
var i;
for (i = 0; i < x.length ;i++) {
course1.push(parseInt(x.elements[i].value));
}
var x = document.getElementById("course2");
var i;
for (i = 0; i < x.length ;i++) {
course2.push(parseInt(x.elements[i].value));
}
//calculate course & student min/max
for (i = 0; i < course0.length; i++) {
if (course0[i] < mincougrade) {
mincougrade = course0[i];
mincougradetext = "course0";
}
if (course0[i] > maxcougrade) {
maxcougrade = course0[i];
maxcougradetext = "course0";
}
if (course0[i] < minstugrade) {
minstugrade = course0[i];
minstugradetext = "student" + [i];
}
if (course0[i] > maxstugrade) {
maxstugrade = course0[i];
maxstugradetext = "student" + [i];
}
}
for (i = 0; i < course1.length; i++) {
if (course1[i] < mincougrade) {
mincougrade = course1[i];
mincougradetext = "course1";
}
if (course1[i] > maxcougrade) {
maxcougrade = course1[i];
maxcougradetext = "course1";
}
if (course1[i] < minstugrade) {
minstugrade = course1[i];
minstugradetext = "student" + [i];
}
if (course1[i] > maxstugrade) {
maxstugrade = course1[i];
maxstugradetext = "student" + [i];
}
}
for (i = 0; i < course2.length; i++) {
if (course2[i] < mincougrade) {
mincougrade = course2[i];
mincougradetext = "course2";
}
if (course2[i] > maxcougrade) {
maxcougrade = course2[i];
maxcougradetext = "course2";
}
if (course2[i] < minstugrade) {
minstugrade = course2[i];
minstugradetext = "student" + [i];
}
if (course2[i] > maxstugrade) {
maxstugrade = course2[i];
maxstugradetext = "student" + [i];
}
}
//calculate course average
for (i = 0; i < course0.length; i++) {
couavg += course0[i];
}
couavg = couavg / course0.length
if (couavg < mincouavg) {
mincouavg = couavg;
mincouavgtext = "course0";
}
if (couavg > maxcouavg) {
maxcouavg = couavg;
maxcouavgtext = "course0";
}
couavg = 0;
for (i = 0; i < course1.length; i++) {
couavg += course1[i];
}
couavg = couavg / course1.length
if (couavg < mincouavg) {
mincouavg = couavg;
mincouavgtext = "course1";
}
if (couavg > maxcouavg) {
maxcouavg = couavg;
maxcouavgtext = "course1";
}
couavg = 0;
for (i = 0; i < course2.length; i++) {
couavg += course2[i];
}
couavg = couavg / course2.length
if (couavg < mincouavg) {
mincouavg = couavg;
mincouavgtext = "course2";
}
if (couavg > maxcouavg) {
maxcouavg = couavg;
maxcouavgtext = "course2";
}
//calculate student average
for (i = 0; i < course0.length; i++) {
stuavgarr[i] += course0[i];
stuavgarr[i] += course1[i];
stuavgarr[i] += course2[i];
}
for (i=0; i < stuavgarr.length; i++) {
stuavgarr[i] = stuavgarr[i] / course0.length;
if (stuavgarr[i] < minstuavg) {
minstuavg = stuavgarr[i];
minstuavgtext = "student" + [i];
}
if (stuavgarr[i] > maxstuavg) {
maxstuavg = stuavgarr[i];
maxstuavgtext = "student" + [i];
}
}
document.getElementById("studmaxgrade").innerHTML = "Student that achieved the max grade is " + maxstugradetext
document.getElementById("studmingrade").innerHTML = "Student that achieved the min grade is " + minstugradetext
document.getElementById("studmaxavg").innerHTML = "Student that achieved the max average is " + maxstuavgtext
document.getElementById("studminavg").innerHTML = "Student that achieved the min average is " + minstuavgtext
document.getElementById("courmaxgrade").innerHTML = "The course in which the max grade is scored is " + maxcougradetext
document.getElementById("courmingrade").innerHTML = "The course in which the min grade is scored is " + mincougradetext
document.getElementById("courmaxavg").innerHTML = "The course in which the max average grade is scored is " + maxcouavgtext
document.getElementById("courminavg").innerHTML = "The course in which the min average grade is scored is " + mincouavgtext
}
</script>

The value of an input is a string, thus a + b will be interpreted as appending one string to another.
If you make sure the first parameter (a in this case) is an integer a + b will result in the two being mathematically adding the two
console.log( '0' + 1 + 2 + 3 + 4 ); //* outputs 01234
console.log( parseInt( 0 ) + 1 + 2 + 3 + 4 ); //* outputs 10
JSFiddle

Ok for a start you seem very confused about
document.getElementById
This does not address a javascript variable at all......
This literally "gets the document element by its id".
Here is an example of how to use it...
<html>
<img id='my_new_selfie' src='me.jpg'>
....
....
<script>
alert (document.getElementById('my_new_selfie').src)
</script>
This would simply pop up an alert with the text that describes the src of the
document object who's id is 'my_new_selfie'
that is....
[me.txt]
The reason that document.getElementById was introduced to javascript was to save developers learning the DOM (document object model) in order to access objects.
It allows you to simply give you object an id and change things about it using the id
In the above example I could use a script or button to change the image source
an example of this might be using the onclick event of another object on the page like a button...
onclick='document.getElementById('my_new_selfie').src='new_pic_of_me.JPG'
It is not used to identify variables in a javascript

How to count the number of section tags in an article tag?

I have been trying to write code that would use an embedded for loop to calculate the number of sections inside of each article (there is more than one so I can't use getID) in a document. When the button is clicked the code works but the numbers it calculates are completely off which means something isn't counting correctly. Here is my function:
<script>
function Calculations() {
var a = document.getElementsByTagName("article");
var s = 0;
var z = 0;
var x;
for (x = 0; x < a.length; x++) {
var cn = a[x].childNodes;
z++
for (i = 0; i < cn.length; i++) {
if (cn[i].nodeType == 1) {
if (cn[i].tagName == "P"); {
s++;
}
}
}
alert("Article " + z + " has " + s + " section.")
s = 0
}
alert("There are " + a.length + " total articles.")
}
</script>
Thank you so much for your help!

making groups with random names in it in javascript

I am new to coding Javascript. I am trying to to shuffle list of names inputted on a textarea. The user selects the number of groups desired, and shuffle on click, then show the divided groups as output result. Below is my code but it is not working as it should be, pls help!
<script>
function ArrayToGroups(source, groups){
var groupList = [];
groupSize = Math.ceil(source.length/groups);
var queue = source;
for(var r = 0; r < groups; r++){
groupList.push(queue.splice(0,groupSize));
}
return groupList;
}
function textSpliter(splitText){
var textInput = document.getElementById("inputText").value;
var splitText = textInput.split(',');
var newList = [];
for(x = 0; x <= splitText.length; x++) {
var random = Math.floor(Math.random() * splitText.length);
var p = splitText[random];
newList.push(p);
splitText.splice(p,groupList);
}
for(var i = 0; i < newList.length; i++){
var s = newList[i];
document.getElementById('resInput').value += s + "\n" ;
}
return splitText;
}
</script>
Below is my input and output textareas
</head>
<body>
<form>
<textarea id="inputText" placeholder="text" rows="10" cols="40"></textarea>
<input type="number" name="number" max="6" value="1" id="groupNumber">
<textarea id="resInput" placeholder="text" rows="10" cols="40"></textarea>
<input type="button" name="Shuffle" value="shuffle" onclick="textSpliter()">
</form>
</body>
</html>

function shuffle() {
// Get list
// Example: element1, element 2, ele ment 3, ...
var list = document.getElementById("inputText").value.replace(/\s*,\s*/g, ",").split(",");
// Get number of groups
var n = parseInt(document.getElementById("groupNumber").value);
// Calculate number of elements per group
var m = Math.floor(list.length / n);
// Enought elements
if (n * m == list.length) {
// Create groups
var groups = new Array();
for (i = 0; i < n; i++) {
groups[i] = new Array();
for (j = 0; j < m; j++) {
// Random
rand = Math.floor(Math.random() * list.length);
// Add element to group
groups[i][j] = list[rand];
// Remove element to list
list.splice(rand, 1);
}
}
// Output
var text = "";
for (i = 0; i < n; i++) {
text += "Group " + (i + 1) + ": ";
for (j = 0; j < m; j++) {
if (j != 0) { text += ", "; }
text += groups[i][j];
}
text += "\n";
}
document.getElementById("resInput").value = text;
} else {
alert("Add more elements");
}
}

I rewrote your code. It's pretty self-explanatory.
FIDDLE
function textSpliter() {
var input = document.getElementById("inputText").value;
var names = input.split(",");
var groupSize = document.getElementById("groupNumber").value;
var groupCount = Math.ceil(names.length / groupSize);
var groups = [];
for (var i = 0; i < groupCount; i++) {
var group = [];
for (var j = 0; j < groupSize; j++) {
var random = Math.floor(Math.random() * names.length);
var name = names[random];
if (name != undefined) {
group.push(name);
names.splice(names.indexOf(name), 1);
}
}
group.sort();
groups.push(group);
}
printGroups(groups);
}
function printGroups(group) {
var output = document.getElementById("resInput");
output.value = "";
for (var i = 0; i < group.length; i++) {
var currentGroup = "";
for (var j = 0; j < group[i].length; j++) {
currentGroup = group[i].join(",");
}
output.value += currentGroup + "\r";
}
}

ES6 version ;-)
http://jsfiddle.net/dLgpny5z/1/
function textSpliter() {
var input = document.getElementById("inputText").value;
var names = input.replace(/\s*,\s*|\n/g, ",").split(",");
var groupSize = document.getElementById("groupNumber").value;
var groupCount = Math.ceil(names.length / groupSize);
var groups = [...Array(groupCount)].map(() => Array());
var i = 0
while (names.length > 0) {
var m = Math.floor(Math.random() * names.length);
groups[i].push(names[m]);
names.splice(m, 1);
i = (i >= groupCount - 1) ? 0 : i + 1
}
printGroups(groups);
}
function printGroups(groups) {
var output = document.getElementById("resInput");
output.value = groups.map(group => group.join(',')).join('\r');
}

Random LocalStorage Jquery

I have a group of divs called "oponente", and if the user do not click on one of them in five seconds the script will choose one randomly. What I dont know how to do is to keep in LocalStorage which div the script had choose. Here is my script, I dont know what to write on 'key name' and so on.
$(document).ready(function () {
$(".oponente").addClass("gray");
var elements = $(".oponente");
var elementCount = elements.size();
var elementsToShow = 1;
var alreadyChoosen = ",";
var i = 0;
while (i < elementsToShow) {
var rand = Math.floor(Math.random() * elementCount);
if (alreadyChoosen.indexOf("," + rand + ",") < 0) {
alreadyChoosen += rand + ",";
setTimeout(function () {
elements.eq(rand).window.localStorage.setItem('key name', 'key name');
}, 5000);
++i;
}
}
});

You can store index of selected one. Then you can get child from the parent with that index number clearly.
Let me simulate
$(document).ready(function () {
$(".oponente").addClass("gray");
var elements = $(".oponente");
var elementCount = elements.size();
var elementsToShow = 1;
var alreadyChoosen = ",";
var i = 0;
while (i < elementsToShow) {
var rand = Math.floor(Math.random() * elementCount);
if (alreadyChoosen.indexOf("," + rand + ",") < 0) {
alreadyChoosen += rand + ",";
setTimeout(function () {
localStorage.setItem('indexOfSelected', selectedDiv.index());
}, 5000);
++i;
}
}
});
Then you can get the selected div with
var indexOfSelected = localStorage.getItem('indexOfSelected');
myDiv = parentDiv.children(":eq("+indexOfSelected+")")
All you need to init a selectedDiv then a parentDiv which is parent of the selectedDiv.

How to remove random image selection and make it linear selection using javascript

The below code selects random images,I want it to select linearly and display the next 8 images in next refresh.
$.fn.preload = function() {
this.each(function(){
$('<img/>')[0].src = this;
});
}
function preloadImg(totalClients)
{
for(var i = 1; i <= totalClients; i++)
{
$('<img src="images/clients/' + i + '.jpg"/>');
}
}
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);
}
function randomClients(totalClients)
{
rarr = getRandoms(8,1,totalClients);
$(".pretty-box").each(function(index)
{
$(this).fadeOut(function(){
src = "images/clients/" + rarr[index] + ".jpg" ;
$(this).attr('src',src);
$(this).fadeIn();
});
});
}
We are able to pick the first 8 images from our array but not the next 8 images.
Can someone help us with this?