# Learn Advanced Array Methods by Building a Statistics Calculator

Hi guys.
Can you explain how does median effects on sorting numbers, when I’m using another array? when i silent my median code, the arrays sorting will be like the first time.
with median:

without median:

Doesn’t median should just sort our array when that function is called?

full code:

``````const getMean = (array) => array.reduce((acc, el) => acc + el, 0) / array.length;

const getMedian = (array) => {
const sorted = array.sort((a, b) => a - b);
const median =
array.length % 2 === 0
? getMean([sorted[array.length / 2], sorted[array.length / 2 - 1]])
: sorted[Math.floor(array.length / 2)];
return median;
}

const getMode = (array) => {
const counts = {};
array.forEach((el) => {
counts[el] = (counts[el] || 0) + 1;
})
if (new Set(Object.values(counts)).size === 1) {
return null;
}
const highest = Object.keys(counts).sort(
(a, b) => counts[b] - counts[a]
)[0];
const mode = Object.keys(counts).filter(
(el) => counts[el] === counts[highest]
);
return mode.join(", ");
}

const getRange = (array) => {
return Math.max(...array) - Math.min(...array);
}

const getVariance = (array) => {
const mean = getMean(array);
const variance = array.reduce((acc, el) => {
const difference = el - mean;
const squared = difference ** 2;
return acc + squared;
}, 0) / array.length;
return variance;
}

const calculate = () => {
const value = document.querySelector("#numbers").value;
const array = value.split(/,\s*/g);
const numbers = array.map(el => Number(el)).filter(el => !isNaN(el));

const mean = getMean(numbers);
const median = getMedian(numbers);
const mode = getMode(numbers);
const range = getRange(numbers);
const variance = getVariance(numbers);

document.querySelector("#mean").textContent = mean;
document.querySelector("#median").textContent = median;
document.querySelector("#mode").textContent = mode;
document.querySelector("#range").textContent = range;
document.querySelector("#variance").textContent = variance;

}
``````

you can see from this picture too

can you give the link to the step? or write the full code (html included) that you are testing?

actually i learned that .sort() method can mutate original array and i didn’t know about it. In the next steps we used .slice() before sort, it made a shallow copy from array and didn’t mutate the original array.

But I need your help for another question.
We didn’t learn about new Set & Object.value & .size.

``````if (new Set(Object.values(counts)).size === 1) {
return null;
}
``````

I know this can delete [1, 1, 1] object value. but how?

html full code:

``````<!DOCTYPE html>
<html lang="en">
<meta charset="utf-8" />
<meta name="viewport" content="width=device-width, initial-scale=1" />
<script src="./script.js"></script>
<title>Statistics Calculator</title>
<body>
<h1>Statistics Calculator</h1>
<p>Enter a list of comma-separated numbers.</p>
<form onsubmit="calculate(); return false;">
<label for="numbers">Numbers:</label>
<input type="text" name="numbers" id="numbers" />
<button type="submit">Calculate</button>
</form>
<div class="results">
<p>
The <dfn>mean</dfn> of a list of numbers is the average, calculated by
taking the sum of all numbers and dividing that by the count of numbers.
</p>
<p class="bold">Mean: <span id="mean"></span></p>
<p>
The <dfn>median</dfn> of a list of numbers is the number that appears in
the middle of the list, when sorted from least to greatest.
</p>
<p class="bold">Median: <span id="median"></span></p>
<p>
The <dfn>mode</dfn> of a list of numbers is the number that appears most
often in the list.
</p>
<p class="bold">Mode: <span id="mode"></span></p>
<p>
The <dfn>range</dfn> of a list of numbers is the difference between the
largest and smallest numbers in the list.
</p>
<p class="bold">Range: <span id="range"></span></p>
<p>
The <dfn>variance</dfn> of a list of numbers measures how far the values
are from the mean, on average.
</p>
<p class="bold">Variance: <span id="variance"></span></p>
<p>
The <dfn>standard deviation</dfn> of a list of numbers is the square
root of the variance.
</p>
<p class="bold">
Standard Deviation: <span id="standardDeviation"></span>
</p>
</div>
</body>
</html>
``````

javascript full code (untill step 36):

``````const getMean = (array) => array.reduce((acc, el) => acc + el, 0) / array.length;

const getMedian = (array) => {
const sorted = array.sort((a, b) => a - b);
const median =
array.length % 2 === 0
? getMean([sorted[array.length / 2], sorted[array.length / 2 - 1]])
: sorted[Math.floor(array.length / 2)];
return median;
}

const getMode = (array) => {
const counts = {};
array.forEach((el) => {
counts[el] = (counts[el] || 0) + 1;
})
if (new Set(Object.values(counts)).size === 1) {
return null;
}
}

const calculate = () => {
const value = document.querySelector("#numbers").value;
const array = value.split(/,\s*/g);
const numbers = array.map(el => Number(el)).filter(el => !isNaN(el));

const mean = getMean(numbers);
const median = getMedian(numbers);

document.querySelector("#mean").textContent = mean;
document.querySelector("#median").textContent = median;
}
``````

a `Set` has the characteristic that it can’t have duplicated elements, so if you do
`new Set([1, 1, 1])` the result is a set `{1}`.
The `size` is similar to the `length` property on arrays, it returns 1 because there is only one element

`Object.values` gives back an array with only the values in the object.

In total, if the object `counts` has the values of the key/value pairs all the same value, then `return null`

1 Like

does that effects on [1, 1, 2] and change it to [1, 2] ? i know rest of the code won’t work.

The set will be `{1, 2}` in that case, removing the duplicate 1

1 Like

Thank you ilenia, You are great!