How to compute the sum and average of elements in an array

Question

I am having problems adding all the elements of an array as well as averaging them out  How would I do this and implement it with the code I currently have  The elements are supposed to be defined as I have it below    lt script type  text javascript  gt     lt   CDATA   var i  var elmt   new Array     elmt 0     0   elmt 1     1   elmt 2     2   elmt 3     3   elmt 4     4   elmt 5     7   elmt 6     8   elmt 7     9   elmt 8     10   elmt 9     11       Problem here for  i   9  i  lt  10  i       document write  The sum of all the elements is         Problem here        The average of all the elements is         Problem here        lt br  gt                gt   lt  script gt

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Average Shortest One Liner    let avg    1 2 3  reduce  a v i   gt  a i v   i 1      Sum Shortest One Liner   let sum    1 2 3  reduce  a b   gt a b

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I had exactly 10 elements  like in the example  so I did     elmt 0    elmt 1    elmt 2    elmt 3    elmt 4      elmt 5    elmt 6    elmt 7    elmt 8    elmt 9      10

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A solution I consider more elegant   const sum   times reduce  a  b    gt  a   b  0   const avg    sum   times length     0   console log  The sum is    sum   The average is    avg

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Not the fastest  but the shortest and in one line is using map    amp  reduce     var average    7 14 21  map function x i arr  return x arr length   reduce function a b  return a   b

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If anyone ever needs it - Here is a recursive average    In the context of the original question  you may want to use the recursive average if you allowed the user to insert additional values and  without incurring the cost of visiting each element again  wanted to  update  the existing average           Computes the recursive average of an indefinite set     param  Iterable lt number gt   set iterable sequence to average     param  number  initAvg initial average value     param  number  initCount initial average count     function average set  initAvg  initCount      if   set     set Symbol iterator       throw Error  must pass an iterable sequence       let avg   initAvg    0    let avgCnt   initCount    0    for  let x of set        avgCnt    1      avg   avg     avgCnt - 1    avgCnt    x   avgCnt        return avg     or  avg  avg  count  avgCnt      average  2  4  6         returns 4 average  4  6   2  1     returns 4 average  6   3  2        returns 4 average       Symbol iterator          yield 2  yield 4  yield 6                               returns 4   How    this works by maintaining the current average and element count  When a new value is to be included you increment count by 1  scale the existing average by  count-1    count  and add newValue   count to the average    Benefits     you don t sum all the elements  which may result in large number that cannot be stored in a 64-bit float   you can  update  an existing average if additional values become available   you can perform a rolling average without knowing the sequence length     Downsides     incurs lots more divisions not infinite - limited to Number MAX SAFE INTEGER items unless you employ BigNumber

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Average of HTML content itens With jQuery or Javascript s querySelector you have direct acess to formated data     Example   lt p gt Elements for an average   lt span class  quot m quot  gt 2 lt  span gt    lt span class  quot m quot  gt 4 lt  span gt       lt span class  quot m quot  gt 2 lt  span gt    lt span class  quot m quot  gt 3 lt  span gt    lt  p gt   So  with jQuery you have var A       m      map function idx    return  parseInt   this  html          get    var AVG   A reduce function a b  return a b     A5 length   See other more 4 ways     to access itens and average it  http   jsfiddle net 4fLWB

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Array prototype avg function fn       fn  fn    function e i  return e       return  this map fn  reduce function a b  return parseFloat a  parseFloat b   0    this length           Then       1   2   3  avg        - gt  OUT   2    age 25   age 26   age 27   avg function e  return e age       OUT   26

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var scores   90  98  89  100  100  86  94           var sum   0          var avg   0          for var i   0  i  lt  scores length i         Taking sum of all the arraylist             sum   sum   scores i                            Taking average                   avg   sum scores length              this is the function to round a decimal no                  var round   avg toFixed                 console log round

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Here is a quick addition to the    Math    object in javascript to add a    average    command to it    Math average   function input      this output   0    for  this i   0  this i  lt  input length  this i          this output  Number input this i          return this output input length      Then i have this addition to the    Math    object for getting the sum   Math sum   function input      this output   0    for  this i   0  this i  lt  input length  this i          this output  Number input this i          return this output      So then all you do is  alert Math sum  5 5 5       alerts    15    alert Math average  10 0 5       alerts    5      And where i put the placeholder array just pass in your variable  The input if they are numbers can be a string because of it parsing to a number

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Let s imagine we have an array of integers like this   var values     0  1  2  3  4  5  6  7  8  9  10  11     The average is obtained with the following formula  A   1 n Sxi   with i   1 to n       So  x1 n   x2 n         xn n  We divide the current value by the number of values and add the previous result to the returned value   The reduce method signature is   reduce callback  default previous value     The reduce callback function takes the following parameters    p   Result of the previous calculation  c   Current value  from the current index  i   Current array element s index value a   The current reduced Array   The second reduce s parameter is the default value      Used in case the array is empty     So the average reduce method will be   var avg   values reduce function p c i a  return p    c a length   0     If you prefer you can create a separate function   function average p c i a  return p    c a length    function sum p c  return p   c      And then simply refer to the callback method signature   var avg   values reduce average 0   var sum  values reduce sum 0     Or Augment the Array prototype directly     Array prototype sum   Array prototype sum    function       return this reduce function p c  return p c  0        It s possible to divide the value each time the reduce method is called     Array prototype avg   Array prototype avg    function        return this reduce function p c i a  return p  c a length   0        Or even better   using the previously defined Array protoype sum    method  optimize the process my calling the division only once     Array prototype avg   Array prototype avg    function        return this sum   this length        Then on any Array object of the scope    2  6  avg      - gt  4  2  6  sum      - gt  8   NB  an empty array with return a NaN wish is more correct than 0 in my point of view and can be useful in specific use cases

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here s your one liner   var average   arr reduce  sum item index arr   gt index     arr length-1 sum item sum item arr length 0

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generally average using one-liner reduce is like this  elements reduce function sum  a i ar    sum    a   return i  ar length-1  ar length  0 0 sum ar length  sum  0     specifically to question asked  elements reduce function sum  a i ar    sum    parseFloat a    return i  ar length-1  ar length  0 0 sum ar length  sum  0     an efficient version is like  elements reduce function sum  a    return sum   a   0   elements length  1     Understand Javascript Array Reduce in 1 Minute http   www airpair com javascript javascript-array-reduce  as  gotofritz pointed out seems Array reduce skips undefined values  so here is a fix    function average arr  var finalstate arr reduce function state a    state sum  a state count  1  return state    sum 0 count 0    return finalstate sum finalstate count    2   6

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I use these methods in my personal library   Array prototype sum   Array prototype sum    function       return this reduce function sum  a    return sum   Number a     0      Array prototype average   Array prototype average    function       return this sum      this length    1       EDIT  To use them  simply ask the array for its sum or average  like    1 2 3  sum        6  1 2 3  average        2

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set your for loop counter to 0     you re getting element 9 and then you re done as you have it now  The other answers are basic math  Use a variable to store your sum  need to cast the strings to ints   and divide by your array length

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I am just building on Abdennour TOUMI s answer   here are the reasons why   1   I agree with Brad  I do not think it is a good idea to extend object that we did not create   2   array length is exactly reliable in javascript  I prefer Array reduce beacuse a  1 3  a 1000  5    now a length would return 1001   function getAverage arry          check if array     if   Object prototype toString call arry        object Array              return 0            var sum   0  count   0       sum   arry reduce function previousValue  currentValue  index  array            if isFinite currentValue                count                return previousValue  parseFloat currentValue                     return previousValue         sum       return count   sum   count   0

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There seem to be an endless number of solutions for this but I found this to be concise and elegant   const numbers    1 2 3 4   const count   numbers length  const reducer    adder  value    gt   adder   value   const average   numbers map x   gt  x count  reduce reducer   console log average      2 5   Or more consisely   const numbers    1 2 3 4   const average   numbers map x   gt  x numbers length  reduce  adder  value    gt   adder   value    console log average      2 5   Depending on your browser you may need to do explicit function calls because arrow functions are not supported   const r   function  adder  value            return adder   value     const m   function  x            return x count     const average   numbers map m  reduce r   console log average      2 5   Or   const average1   numbers      map function  x            return x count               reduce function  adder  value            return adder   value      console log average1

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On evergreen browsers you can use arrow functions avg    1 2 3  reduce  a b    gt   a b    Running it 100 000 times  the time difference between the for loop approach and reduce is negligible    x000D   x000D  s Date now   for i 0 i lt 100000 i     n  1 2 3   a n reduce  a b    gt   a b     n length    x000D  console log  100k reduce took      Date now  -s     ms     x000D   x000D  s Date now   for i 0 i lt 100000 i    n  1 2 3   nl n length  a 0  for j nl-1 j gt 0 j--  a a n j    a nl    x000D  console log  100k for loop took      Date now  -s     ms     x000D   x000D  s Date now   for i 0 i lt 1000000 i    n  1 2 3   nl n length  a 0  for j nl-1 j gt 0 j--  a a n j    a nl    x000D  console log  1M for loop took      Date now  -s     ms     x000D   x000D  s Date now   for i 0 i lt 1000000 i     n  1 2 3   a n reduce  a b    gt   a b     n length    x000D  console log  1M reduce took      Date now  -s     ms     x000D   x000D      x000D     RESULT on Chrome 51 x000D     100k reduce took 26ms  x000D     100k for loop took 35ms  x000D     10M for loop took 126ms  x000D     10M reduce took 209ms  x000D      x000D   x000D   x000D

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I would recommend D3 in this case  It is the most readable  and provides 2 different kinds of averages   let d3   require  d3    let array    1 2 3 4   let sum   d3 sum array     10 let mean   d3 mean array     2 5 let median   d3 median array

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var arr    1 2 3 4 5   function avg arr     var sum   0    for  var i   0  i  lt  arr length  i          sum    parseFloat arr i         return sum   i      avg arr             3  This works with strings as numbers or numbers in the array

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You can also use lodash    sum array  and   mean array  in Math part  also have other convenient stuff      sum  4  2  8  6         gt  20   mean  4  2  8  6         gt  5

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I think we can do like  var k elmt reduce function a b  return parseFloat a parseFloat b      var avg k elmt length   console log avg     I am using parseFloat twice because when  1  you add  a 9 b  1   number then result will be  91  but we want addition  so i used parseFloat  2 When addition of  a 9 parseFloat  1   happen though result will be  10  but it will be in string which we don t want so again i used parseFloat   I hope i am clear  Suggestions are welcome

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If you are in need of the average and can skip the requirement of calculating the sum  you can compute the average with a single call of reduce      Assumes an array with only values that can be parsed to a Float var reducer   function cumulativeAverage  currentValue  currentIndex         1  multiply average by currentIndex to find cumulative sum of previous elements      2  add currentValue to get cumulative sum  including current element      3  divide by total number of elements  including current element  zero-based index   1    return  cumulativeAverage   currentIndex   parseFloat currentValue    currentIndex   1    console log  1  2  3  4  5  6  7  8  9  10  reduce reducer  0         gt  5 5 console log    reduce reducer  0         gt  0 console log  0  reduce reducer  0         gt  0 console log    reduce reducer  0         gt  0 console log       reduce reducer  0         gt  0 console log    reduce reducer  0         gt  0

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var sum   0  for  var i   0  i  lt  elmt length  i          sum    parseInt  elmt i   10      don t forget to add the base    var avg   sum elmt length   document write   The sum of all the elements is      sum     The average is      avg      Just iterate through the array  since your values are strings  they have to be converted to an integer first  And average is just the sum of values divided by the number of values

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I think this may be a direct solution to calculate the average with a for loop and function   var elmts    0  1  2  3  4  5  6  7  8  9  10  11    function average arr        var total   0      for  var i   0  i  lt  arr length  i              total    arr i                 console log Math round total arr length       average elmts

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Here is my rookie way of simply finding the avg  Hope this helps somebody   function numAvg num       var total   0      for var i   0 i  lt  num length  i               total  num i             return total num length

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Just for kicks   var elmt    0  1  2 3  4  7  8  9  10  11   l   elmt length  i   -1  sum   0  for      i  lt  l  sum    elmt i         document body appendChild document createTextNode  The sum of all the elements is      sum     The average of all the elements is       sum   l

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In ES6-ready browsers this polyfill may be helpful   Math sum       a    gt  Array prototype reduce call a  a b    gt  a b   Math avg       a    gt  this sum    a  a length    You can share same call method between Math sum Math avg  and Math max such as  var maxOne   Math max 1 2 3 4     4    you can use Math sum as  var sumNum   Math sum 1 2 3 4     10   or if you have an array to sum up you can use   var sumNum   Math sum apply null  1 2 3 4      10   just like   var maxOne   Math max apply null  1 2 3 4      4

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Start by defining all of the variables we plan on using  You ll note that for the numbers array  I m using the literal notation of    as opposed to the constructor method array    Additionally  I m using a shorter method to set multiple variables to 0   var numbers       count   sum   avg   0    Next I m populating my empty numbers array with the values 0 through 11  This is to get me to your original starting point  Note how I m pushing onto the array count    This pushing the current value of count  and then increments it for the next time around   while   count  lt  12       numbers push  count        Lastly  I m performing a function  for each  of the numbers in the numbers array  This function will handle one number at a time  which I m identifying as  n  within the function body   numbers forEach function n     sum    n     avg   sum   numbers length        In the end  we can output both the sum value  and the avg value to our console in order to see the result      Sum  66  Avg  5 5 console log   Sum      sum      Avg      avg      See it in action online at http   jsbin com unukoj 3 edit

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ES6  x000D   x000D  const average   arr   gt  arr reduce    p  c     gt  p   c  0     arr length       const result   average    4  4  5  6  6         5      console log result   x000D   x000D   x000D

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One sneaky way you could do it although it does require the use of  the much hated  eval     var sum   eval elmt join        avg   sum   elmt length  document write  The sum of all the elements is      sum     The average of all the elements is      avg     lt br  gt       Just thought I d post this as one of those  outside the box  options  You never know  the slyness might grant you  or taketh away  a point

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Calculating average  mean  using reduce and ES6   const average   list   gt  list reduce  prev  curr    gt  prev   curr    list length   const list    0  10  20  30  average list     15

[javascript] How to compute the sum and average of elements in an array?

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