javascript - Find if numbers in an array are between two numbers and output number of values that are between - Stack Overflow

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I've been trying for the past few hours to find out how to find numbers in array that are between 2 numbers and I don't know where to go. What do I need to do? 18 and 20 are just placeholder numbers, feel free to use any numbers you want.

function start() {
    var array = [18, 23, 20, 17, 21, 18, 22, 19, 18, 20];
    var lower = 18;
    var upper = 20;

    if (need help here) {
        alert('Yes');
    } else {
        alert('No');
    }

    document.getElementById('listOfvalues').innerHTML = ('There are ' + ___ + ' numbers that are between the two numbers);
    document.getElementById('numberExist').innerHTML = numberExist;
}

I know I haven't provided much, but I will go crazy if I try to do this myself

I've been trying for the past few hours to find out how to find numbers in array that are between 2 numbers and I don't know where to go. What do I need to do? 18 and 20 are just placeholder numbers, feel free to use any numbers you want.

function start() {
    var array = [18, 23, 20, 17, 21, 18, 22, 19, 18, 20];
    var lower = 18;
    var upper = 20;

    if (need help here) {
        alert('Yes');
    } else {
        alert('No');
    }

    document.getElementById('listOfvalues').innerHTML = ('There are ' + ___ + ' numbers that are between the two numbers);
    document.getElementById('numberExist').innerHTML = numberExist;
}

I know I haven't provided much, but I will go crazy if I try to do this myself

• javascript
• arrays

Share Improve this question Follow edited Apr 16, 2017 at 11:58 Ghrafkly asked Apr 16, 2017 at 11:48 GhrafklyGhrafkly 11544 silver badges1212 bronze badges 4

• 1 please add the wanted result as well. – Nina Scholz Commented Apr 16, 2017 at 12:00
• The final output will say the number of values between those 2 values. So in my example where I used 18 and 20, the final result should be '6'. This would vary with different values as constraints – Ghrafkly Commented Apr 16, 2017 at 12:09
• 1 please highlight, how do you get 6. – Nina Scholz Commented Apr 16, 2017 at 12:14
• Well, between 18 and 20, there is 18, 20, 18, 19, 18, 20. If, let's say the numbers were 20 and 30, 5 numbers fit the criteria, 23, 20, 21, 22, 20. Hope this helps – Ghrafkly Commented Apr 16, 2017 at 12:18

Add a ment  | 

5 Answers 5

Sorted by: Reset to default 4

var lower = 18;
var upper = 20;
var array = [18, 23, 20, 17, 21, 18, 22, 19, 18, 20];
var between = array.filter(function(item) {
  return (item > lower && item < upper);
});

var listOfvalues=[];
    for(var i=0;i<array.length;i++){
       if (array[i]>18 && array[i]<20) {
           listOfvalues.push(array[i]);           
       } 
    }


    document.getElementById('listOfvalues').innerHTML = 'There are ' + listOfvalues.length + ' numbers that are between the two numbers';

You could test, if the value is in the given range and count it.

var array = [18, 23, 20, 17, 21, 18, 22, 19, 18, 20],
    lower = 18,
    upper = 20,
    result = array.reduce(function (r, a) {
        return r + (a >= lower && a <= upper);
    }, 0);

console.log(result);

ES6

var array = [18, 23, 20, 17, 21, 18, 22, 19, 18, 20],
    lower = 18,
    upper = 20,
    result = array.reduce((r, a) => r + (a >= lower && a <= upper), 0);

console.log(result);

How does Array#reduce work in this case?

You have an accumulator for the result, denoted as r and an actual value of the iteration, denoted as a. The returned result is the sum of the former count and the ckeck, if the value is in the given range.

    r       a   return   ment
------  ------  ------  --------
    0      18       1   in range
    1      23       1
    1      20       2   in range
    2      17       2
    2      21       2
    2      18       3   in range
    3      22       3
    3      19       4   in range
    4      18       5   in range
    5      20       6   in range
    6                   result

Some thoughts, all in ES6 style.

You could use a callback for Array#reduce with a closure over lower and upper, like

var array = [18, 23, 20, 17, 21, 18, 22, 19, 18, 20],
    getCountInRange = (lower, upper) => (r, a) => r + (a >= lower && a <= upper);

console.log(array.reduce(getCountInRange(18, 20), 0));

or you could use a function which takes the array, lower and upper and returns the count.

var array = [18, 23, 20, 17, 21, 18, 22, 19, 18, 20],
    getCountInRange = (array, lower, upper) => array.reduce((r, a) => r + (a >= lower && a <= upper), 0);

console.log(getCountInRange(array, 18, 20));

One approach is the following:

// a changed (hopefully meaningful) name for the function,
// lower: Number, the lower-boundary,
// upper: Number, the upper-boundary,
// haystack: Array, the array of values:
function numbersBetween(lower, upper, haystack) {

  // if every value of the Array is, or can be coerced to,
  // a Number then we continue to work with that Array:
  if (haystack.every(value => Number(value))) {

    // Here we use Array.prototype.filter() to filter the
    // values of the Array according the function:
    return haystack.filter(

      // here we use an Arrow function, since we don't need
      // to use a 'this'; here we retain the current value ('n')
      // in the Array if that Number is greater than the
      // lower-boundary and lower than the upper-boundary:
      n => n > lower && n < upper
    );
  }

  // otherwise, if not every value is, or can be coerced,
  // to a Number we simply return an empty Array:
  return [];
}

// this caches the element with the id of 'output':
let list = document.getElementById('output'),

  // we create an <li> element:
  li = document.createElement('li'),

  // we create a document fragment:
  fragment = document.createDocumentFragment(),

  // and an empty uninitialised variable:
  clone;

// we call the numbersBetween function, passing in the relevant
// boundaries and the Array:
numbersBetween(7, 20, [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 15])

// because the function returns an Array (either an empty Array or
// an Array with values), we can chain the function using
// Array.prototype.forEach():
.forEach(

  // here we use another Arrow function expression:
  num => {

    // clone the created <li> element and assign it
    // the 'clone' variable:
    clone = li.cloneNode();

    // set the clone's textContent to be equal to
    // the current Array-element of the Array over
    // which we're iterating:
    clone.textContent = num;

    // and append that cloned-element to the
    // document.fragment:
    fragment.appendChild(clone);
  });

// this could be used in the last iteration of the
// Array.prototype.forEach() method, but because it
// generates no errors (an empty document fragment
// can be appended to an element without consequence),
// we perform this step here, appending the document
// fragment to the cached 'list' element which appends
// the nodes contained within the document fragment to
// the specified parent-node (list):
list.appendChild(fragment);

function numbersBetween(lower, upper, haystack) {
  if (haystack.every(value => Number(value))) {

    return haystack.filter(
      n => n > lower && n < upper
    );
  }
  return [];
}

let list = document.getElementById('output'),
  li = document.createElement('li'),
  fragment = document.createDocumentFragment(),
  clone;

numbersBetween(7, 20, [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 15]).forEach(
  num => {
    clone = li.cloneNode();
    clone.textContent = num;
    fragment.appendChild(clone);
  });
list.appendChild(fragment);

#output::before {
  content: 'The following numbers were found:';
  display: list-item;
  list-style-type: none;
}

#output:empty::before {
  content: '';
}

<ul id="output"></ul>

JS Fiddle demo.

Providing a filtered solution to Wei's answer

var array = [18, 23, 20, 17, 21, 18, 22, 19, 18, 20];
var lower = 18;
var upper = 20;

var result = array.filter(function(item) {
  return item >= lower && item <= upper;
});

document.getElementById('listOfvalues').innerHTML = ('There are ' + result.length + ' numbers that are between the two numbers);

In short, use the filter function to return results according to your low and high boundaries. Print the length of the returned array of values.

For the if/else statement you can do by yourself.

Edit: Added link to filter

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