Finding the average of an array using JS

Question

I ve been looking and haven t found a simple question and answer on stack overflow looking into finding the average of an array    This is the array that I have  var grades    80  77  88  95  68     I first thought that the answer to this problem would be something like this    var avg    grades   grades length    grades length console log avg    However this gave me an output of NaN   So then I tried this    for   var i   0  i  lt  grades length  i          var avg    grades i    grades length    grades length   console log avg    This gave me an output of 68   I m not sure why    So with this I have two questions  1  Why was my output 68  and 2  Could somebody help me out with actually finding the average of an array

User · Answer

The average function you can do is   const getAverage    arr    gt  arr reduce  p  c    gt  p   c  0    arr length   Also  I suggest that use the popoular open source tool  eg  Lodash   const     require  lodash   const getAverage    arr    gt    chain arr    sum     divide arr length    round 1    value

User · Answer

It can simply be done with a single reduce operation as follows    x000D   x000D  var avg    1 2 3 4  reduce  p c   a    gt  p   c a length 0   x000D  console log avg  x000D   x000D   x000D

User · Answer

For the second part of your question you can use reduce to good effect here    x000D   x000D  const grades    80  77  88  95  68   x000D   x000D  function getAvg grades    x000D    const total   grades reduce  acc  c    gt  acc   c  0   x000D    return total   grades length  x000D    x000D   x000D  const average   getAvg grades   x000D  console log average   x000D   x000D   x000D    The other answers have given good insight into why you got 68  so I won t repeat it here

User · Answer

With ES6 you can turn Andy s solution into as a one-liner    x000D   x000D  let average    array    gt  array reduce  a  b    gt  a   b    array length  x000D  console log average  1 2 3 4 5     x000D   x000D   x000D

User · Answer

You calculate an average by adding all the elements and then dividing by the number of elements   var total   0  for var i   0  i  lt  grades length  i          total    grades i     var avg   total   grades length    The reason you got 68 as your result is because in your loop  you keep overwriting your average  so the final value will be the result of your last calculation  And your division and multiplication by grades length cancel each other out

User · Answer

Writing the function for average yourself is crazy  That s why modules exist  I found math js  In my HTML file      lt script src  http   cdnjs cloudflare com ajax libs mathjs 3 2 1 math min js  gt  lt  script gt     or you can download it   In my JS code   math mean  1 2 3       2 math mean 1 2 3     the same math mean grades

User · Answer

One liner challange accepted  const average   arr   gt  arr reduce  sume  el    gt  sume   el  0    arr length   and then  average  1 2 3 4       2 5

User · Answer

You can use map reduce functions of javascript to find average  Reduce will sum them up  and map will find average   var avg   grades map  c  i  arr    gt  c   arr length  reduce  p  c    gt  c   p

User · Answer

The MacGyver way just for lulz   x000D   x000D  var a    80  77  88  95  68   x000D   x000D  console log eval a join       a length  x000D   x000D   x000D

User · Answer

There s no built in function  but you can use this to get the sum    Array prototype sum   function         return this reduce function a b  return a b          then divide by the arrays length  e g    var arr    1 2 3 4 5  console log arr sum     arr length

User · Answer

answer to your 1  question   for   var i   0  i  lt  grades length  i          var avg    grades i    grades length    grades length     avg is declared in each loop  Thus  at the end of the loop  avg has the value of the last item in the array   68  5   5

User · Answer

var total   0 grades forEach function  grade        total    grade             console log total   grades length

[javascript] Finding the average of an array using JS

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