How to count number of times an item is in an array

Question

I've decided to just try again from the start since I'm a bit more awake now and go over building this step by step. i've looked at some of the answers and there seems to be many ways one could go about this. I'm trying to do this using what I've learned so far. I've learned about variables, basic functions, objects, arrays, 'this' and the push method. I know for, while, do while, for in loops, though the for loop is the one I understand the best.

Here is my new approach to building this, I know it's unnecessarily long but I want to be able to get a basic understanding of how to piece the different things I've learned together in a very simple way. This is more about learning how to go about building simple programs. Then I would proceed in fine-tuning the program to make it more concise and clever. If you could have a look and tell me how I would proceed with what I've got so far...

Here is the code, Ideally I want to run a function when there's a new 'visitor' that asks for their name and number. Then create a new 'customer' object with the given name and number and push it to a 'visitors' array. once I've successfully figured that out I would use loops to check the array if the visitor is new or not, and update their number of visits everytime they come.

//array that will contain 'Customer' objects
var visitors = [john];

//Customer object
function Customer(name, phonenumber){
  this.name = name;
  this.phonenumber = phonenumber;
//will eventually add a "visits" method logging number of visits

}

var john = new Customer("john smith", "333");

//visitor funtion that runs everytime there is a new visitor
var visitor = function(){

  //visitor does not have a set name or number yet
  var userNumber = "variable userNumber is currently equal to " + 0;
  var userName = "variable userName is currently set to " + undefined;
  console.log(userName, userNumber);

  //ask for visitor name and number
  var askNumber = prompt("type your number");
  var askName = prompt("what is your name?");

  //store user name and number in two variables
  var userNumber = "variable 'userNumber' is now equal to " + askNumber; 
  var userName = "variable userName is now set to " + askName;

  //print out the new variables 
  console.log(userNumber);
  console.log(userName);

  //print who the phone number belongs to, this lets me see that the above code worked correctly
  var userNumber = askNumber;
  var userName = askName;
  console.log("Phone number " + userNumber + " belongs to " + userName);

  //make new customer object with the given name and number
  var userNumber = new Customer();
  userNumber.name = askName;
  userNumber.phonenumber = askNumber;

  console.log("properties of " + userNumber);  

};

the last bit returns "properties of [object, object]" why?

Answer 1

No need to complicate things here's an simple way, just add a count function that search how many times user has enter

 var list = ["111", "222", "333", "444", "555", "666"];
var test = function(input){
  var info = prompt("hi " + input + " what is your name?");
  var check=0;
    for(i=0; i< list.length; i++){
        if( info === list[i]){
           check=1;
           break;
          }
         }

       list.push(info);

       if(check==1){
             count(info);
       }

    }
 function count(info){ 
       var count=0;
       for(i=0; i< list.length; i++){
             if(list[i]===info)
                  count++;
               }
       console.log(count);
      }
    }

Answer 2

I will give you a short function to check how many times a specific value is at the array:

function countHowManyTimesAValueIsOnArray(arr, valueToCheck){
    return  arr.filter(function(arrayValueToCompare){
        return arrayValueToCompare === valueToCheck;
    }).length
}

Attention for the use of '===' instead of '=='. This will compare the value considering its type. 222 will not be found as "222"

Answer 3

I've decided to just try again from the start since I'm a bit more awake now and go over building this step by step. i've looked at some of the answers and there seems to be manyt ways one could go about this. I'm trying to do this using what I've learned so far. I've learned about variables, basic functions, objects, arrays, 'this' and the push method. I know for, while, do while, for in loops, though the for loop is the one I understand the best.

Here is my new approach to building this, I know it's unnecessarily long but I want to be able to get a basic understanding of how to piece the different things I've learned together in a very simple way. This is more about learning how to go about building simple programs. Then I would proceed in fine-tuning the program to make it more concise and clever. If you could have a look and tell me how I would proceed with what I've got so far...

Here is the code, Ideally I want to run a function when there's a new 'visitor' that asks for their name and number. Then create a new 'customer' object with the given name and number and push it to a 'visitors' array. once I've successfully figured that out I would use loops to check the array if the visitor is new or not, and update their number of visits everytime they come.

//array that will contain 'Customer' objects
var visitors = [john];

//Customer object
function Customer(name, phonenumber){
  this.name = name;
  this.phonenumber = phonenumber;
//will eventually add a "visits" method logging number of visits

}

var john = new Customer("john smith", "333");

//visitor funtion that runs everytime there is a new visitor
var visitor = function(){

  //visitor does not have a set name or number yet
  var userNumber = "variable userNumber is currently equal to " + 0;
  var userName = "variable userName is currently set to " + undefined;
  console.log(userName, userNumber);

  //ask for visitor name and number
  var askNumber = prompt("type your number");
  var askName = prompt("what is your name?");

  //store user name and number in two variables
  var userNumber = "variable 'userNumber' is now equal to " + askNumber; 
  var userName = "variable userName is now set to " + askName;

  //print out the new variables 
  console.log(userNumber);
  console.log(userName);

  //print who the phone number belongs to, this lets me see that the above code worked correctly
  var userNumber = askNumber;
  var userName = askName;
  console.log("Phone number " + userNumber + " belongs to " + userName);

  //make new customer object with the given name and number
  var userNumber = new Customer();
  userNumber.name = askName;
  userNumber.phonenumber = askNumber;

  console.log("properties of " + userNumber);  

};

the last bit returns "properties of [object, object]" why?

Answer 4

n is number of costumer

Initially array is [0,0,0,.....n times]

All values are 0 because no costumer has visited the shop.

For n=5 array would look like

var a=[0,0,0,0,0];

1)To solve this problem in array.

2)Suppose we have array of size n.

3)then index of the array will be 0...n-1

4)So we can map id of costumer to the index.

5)And value will keep count of the number of visit for the index.

6)a[5]=11; here 5 is index and 11 is value

7)For our problem if customer with id i we increment a[i]=a[i]+1 if he visits .

8) Then we can check

if(a[i]+1 === 5) {
   console.log("Custumer "+ i + " get a free coffee");
   a[i]=0;
}
else {
   a[i]=a[i]+1;
}

Answer 5

Try including utilization of input elements; set visits count as value of property id, info at object list; call test with value of input element : id ; or at prompt : info . At five visits , display coffee , reset value of id to 0.

var list = {
  "111": 0,
  "222": 0,
  "333": 0,
  "444": 0,
  "555": 0,
  "666": 0
};

var test = function test(id) {
  coffee.innerHTML = "";
  var info;
  if (id.length > 0 && !/^(\s)/.test(id)) {
    if (list.hasOwnProperty(id)) {
      ++list[id];

    } else {
      list[id] = 1;
    }
    info = confirm("hi " + id + " this is your " + list[id] + " visit");
  } else {
    info = prompt("hi, please enter an id");
    if (!!info && !/^(\s)/.test(info) && list.hasOwnProperty(info)) {
      list[info] = 1;
      confirm("hi " + info + " this is your " + list[info] + " visit");
    } else {
      info = prompt("hi, please input a different id");
      if (!!info && !/^(\s)/.test(info) && !list.hasOwnProperty(info)) {
        list[info] = 1;
        confirm("hi " + info + " this is your " + list[info] + " visit");
      }
    };
    alert("please try a different id")
  };

  for (var id in list) {
    if (list[id] === 5) {
      alert("hi " + id + ", thanks for visting " + list[id] + " times");
      coffee.innerText = "☕";
      list[id] = 0;
      break;
    }
  };

  console.log(list);

};

var inputs = document.querySelectorAll("input");
var coffee = document.getElementById("coffee");
coffee.style.fontSize = "5em";

inputs[1].onclick = function(e) {
  test(inputs[0].value)
};

<input type="text" placeholder="please enter id" value="" />
<input type="button" value="click" />
<div id="coffee"></div>

Answer 6

I would solve the problem by storing the visit count in a dictionary that maps each customer's ID to the number of times they have visited. The dictionary is initially empty. When you look up an ID in the dictionary for the first time, you'll get undefined, which tells you that you must initialize the value.

The following demonstration has a couple of buttons that you can use to make Alice or Bob visit the shop. Click on the blue button at the bottom to start the demo.

function message(s) {  // Simple output for a code snippet.
  document.getElementById('display').innerHTML += s + '<br />';
}

var coffeeCount = {};  // Stores the number of visits by each customer.

function customerVisit(id) {  // Called when a customer visits.
  if (coffeeCount[id] === undefined) {  // Check for first visit.
    coffeeCount[id] = 0;                // Initialize the visit count.
  } 
  var count = ++coffeeCount[id];        // Increment the visit count.
  message(id+': '+count+' visit'+(count == 1 ? '' : 's'));
  if (count % 5 == 0) {                 // Check for free coffee.
    message('&rarr; Free coffee for customer '+id+'!');
  } 
}

<button onclick="customerVisit('Alice')">Alice</button>

<button onclick="customerVisit('Bob')">Bob</button>

<div id="display"></div>

Answer 7

heres an algorithm :

Use an object to store the user no. and the count. like :

{"222":"3","444":"1"}

this means 222 has visited 3 times and 444 visited once. now every time a user checks in:

1. see if the key with the user's number exists, if yes increment the count. if no, add a new entry with count = 1.
2. check if the number is 5, if yes get free coffee and reset count to zero. skip if no.

Answer 8

Not only did you confuse yourself, but you crashed the browser! :-)

(The for loop never terminates because you push a new value to the list on every iteration.)

I could tell you what's wrong with the code in more detail, but you'll learn a lot more if you chase it down yourself. So what you need now is to learn the art of debugging.

Add a debugger statement at the beginning of your test() function:

var list = ["111", "222", "333", "444", "555", "666"];

var test = function(input){
    debugger;
    var info = prompt("hi " + input + " what is your name?");
    for(i=0; i< list.length; i++){
        if( info === list.length[i]){
            console.log(list[i]);
        }
        else{
            list.push(info);
        }
        console.log(list);
    }

}

Now run test() and it will stop in the debugger at that statement. Look at the different panels in the debugger - you can view your variables and other stuff. Find the place where it has controls to let you step through your code. Single-step through the code and look at the variables as you go. You will soon discover what the problems are. In most browsers there are also keyboard shortcuts to let you step through the code more easily.

If you use Chrome, here is an introduction to the Chrome DevTools. There are similar tutorials for the other browsers too.