Better way to sum a property value in an array

Question

I have something like this   scope traveler                    description   Senior   Amount  50                  description   Senior   Amount  50                  description   Adult   Amount  75                  description   Child   Amount  35                  description   Infant   Amount  25        Now to have a total Amount of this array I m doing something like this   scope totalAmount   function           var total   0         for  var i   0  i  lt   scope traveler length  i                    total   total    scope traveler i  Amount                       return total     It s easy when is only one array  but I have others arrays with a different property name that I would like to sum  I would be happier If I could do something like this   scope traveler Sum   Amount      But I don t know how to go through this in a way that I could reuse it in the future like this   scope someArray Sum   someProperty

User · Answer

Here is a one-liner using ES6 arrow functions   const sumPropertyValue    items  prop    gt  items reduce  a  b    gt  a   b prop   0       usage  const cart items      quantity  3    quantity  4    quantity  2     const cart total   sumPropertyValue cart items   quantity

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Alternative for improved readability and using Map and Reduce   const traveler            description   Senior   amount  50           description   Senior   amount  50           description   Adult   amount  75           description   Child   amount  35           description   Infant   amount  25        const sum   traveler    map item   gt  item amount     reduce  prev  curr    gt  prev   curr  0     Re-useable function   const calculateSum    obj  field    gt  obj    map items   gt  items attributes field      reduce  prev  curr    gt  prev   curr  0

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How to sum array of object using Javascript  const traveler          description   Senior   Amount  50        description   Senior   Amount  50        description   Adult   Amount  75        description   Child   Amount  35        description   Infant   Amount  25         x000D   x000D  const traveler     x000D         description   Senior   Amount  50   x000D         description   Senior   Amount  50   x000D         description   Adult   Amount  75   x000D         description   Child   Amount  35   x000D         description   Infant   Amount  25    x000D     x000D  function sum arrayData  key   x000D     return arrayData reduce  a b    gt    x000D    return  Amount   a Amount   b Amount  x000D     x000D    x000D  console log sum traveler   x000D   x000D   x000D

User · Answer

I thought I d drop my two cents on this  this is one of those operations that should always be purely functional  not relying on any external variables  A few already gave a good answer  using reduce is the way to go here   Since most of us can already afford to use ES2015 syntax  here s my proposition   const sumValues    obj    gt  Object keys obj  reduce  acc  value    gt  acc   obj value   0     We re making it an immutable function while we re at it  What reduce is doing here is simply this   Start with a value of 0 for the accumulator  and add the value of the current looped item to it   Yay for functional programming and ES2015

User · Answer

I m not sure this has been mentioned yet  But there is a lodash function for that  Snippet below where value is your attribute to sum is  value      sumBy objects   value      sumBy objects  function o    return o value        Both will work

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From array of objects  function getSum array  column    let values   array map  item    gt  parseInt item column      0    return values reduce  a  b    gt  a   b     foo         a  1  b            a  null  b  2        a  1  b  2        a  1  b  2       getSum foo  a     3 getSum foo  b     6

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I know that this question has an accepted answer but I thought I d chip in with an alternative which uses array reduce  seeing that summing an array is the canonical example for reduce    scope sum   function items  prop       return items reduce  function a  b           return a   b prop          0        scope travelerTotal    scope sum  scope traveler   Amount      Fiddle

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I was already using jquery  But I think its intuitive enough to just have   var total amount   0     each traveler  function  i  v     total amount    v Amount         This is basically just a short-hand version of  akhouri s answer

User · Answer

It s working for me in TypeScript and JavaScript    x000D   x000D  let lst     x000D         description  Senior   price  10   x000D         description  Adult   price  20   x000D         description  Child   price  30  x000D     x000D  let sum   lst map o   gt  o price  reduce  a  c    gt    return a   c     x000D  console log sum   x000D   x000D   x000D    I hope is useful

User · Answer

You can do the following    scope traveler map o  gt o Amount  reduce  a c   gt a c

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Here s a solution I find more flexible   function sumOfArrayWithParameter  array  parameter      let sum   null    if  array  amp  amp  array length  gt  0  amp  amp  typeof parameter      string         sum   0      for  let e of array  if  e  amp  amp  e hasOwnProperty parameter   sum    e parameter         return sum      To get the sum  simply use it like that   let sum   sumOfArrayWithParameter someArray   someProperty

User · Answer

can also use Array prototype forEach    let totalAmount   0   scope traveler forEach  data   gt  totalAmount   totalAmount   data Amount   return totalAmount

User · Answer

I always avoid changing prototype method and adding library so this is my solution   Using reduce Array prototype method is sufficient       operator for casting to Number items reduce  a  b    gt   a    b price  0

User · Answer

Just another take  this is what native JavaScript functions Map and Reduce were built for  Map and Reduce are powerhouses in many languages     var traveler     description   Senior   Amount  50                    description   Senior   Amount  50                    description   Adult   Amount  75                    description   Child   Amount  35                    description   Infant   Amount  25     function amount item     return item Amount     function sum prev  next     return prev   next     traveler map amount  reduce sum        gt  235      or use arrow functions traveler map item   gt  item Amount  reduce  prev  next    gt  prev   next        Note  by making separate smaller functions we get the ability to use them again       Example of reuse     Get only Amounts greater than 0      Also  while using Javascript  stick with camelCase     If you do decide to go against the standards      then maintain your decision with all keys as in          description   Senior   Amount  50       would be       Description   Senior   Amount  50     var travelers     description   Senior   amount  50                    description   Senior   amount  50                    description   Adult   amount  75                    description   Child   amount  35                    description   Infant   amount  0         Directly above Travelers array I changed  Amount  to  amount  to match standards   function amount item     return item amount     travelers filter amount        gt    description   Senior   amount  50           description   Senior   amount  50           description   Adult   amount  75           description   Child   amount  35           Does not include  Infant  as 0 is falsey

User · Answer

Use reduce with destructuring to sum Amount  const traveler         description   Senior   Amount  50        description   Senior   Amount  50        description   Adult   Amount  75        description   Child   Amount  35        description   Infant   Amount  25        console log traveler reduce  n   Amount     gt  n   Amount  0

User · Answer

Updated Answer  Due to all the downsides of adding a function to the Array prototype  I am updating this answer to provide an alternative that keeps the syntax similar to the syntax originally requested in the question   class TravellerCollection extends Array       sum key            return this reduce  a  b    gt  a    b key     0   0           const traveler   new TravellerCollection             description   Senior   Amount  50          description   Senior   Amount  50          description   Adult   Amount  75          description   Child   Amount  35          description   Infant   Amount  25         console log traveler sum  Amount         gt  235   Original Answer  Since it is an array you could add a function to the Array prototype   traveler            description   Senior   Amount  50          description   Senior   Amount  50          description   Adult   Amount  75          description   Child   Amount  35          description   Infant   Amount  25        Array prototype sum   function  prop        var total   0     for   var i   0   len   this length  i  lt   len  i               total    this i  prop            return total    console log traveler sum  Amount      The Fiddle  http   jsfiddle net 9BAmj

[javascript] Better way to sum a property value in an array

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