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spinaka's avatar
spinaka
New Contributor III
4 years ago
Solved

Cumulative sum of a value in an array

Hi Everyone, I need help on an expression solution. The “sum” should be the sum of the value(s) of “key2” from previous records till the current record within the array. I’m trying to make it usi...
expression_language
  • bojanvelevski's avatar
    bojanvelevski
    4 years ago

    Here’s a corrected version of the expression:

    $array.map((x,index)=> index==0 ? x.extend({sum:x.key2}) : x.extend({sum:$array.slice(0,index+1).reduce((acc,curr)=> acc+curr.key2,0)}))

    Let me know if this works for you, and I will explain in details on how the expression works.

spinaka's avatar
spinaka
New Contributor III
4 years ago

Hi @bojanvelevski, Thanks for the response.
This Aggregation just gives the sum of all the values that is 60., but we need the cumulative sum in every record as shown in the example output.

sum = sum in the previous record + key2 in the current record.

bojanvelevski's avatar
bojanvelevski
Valued Contributor
4 years ago

Here’s a corrected version of the expression:

$array.map((x,index)=> index==0 ? x.extend({sum:x.key2}) : x.extend({sum:$array.slice(0,index+1).reduce((acc,curr)=> acc+curr.key2,0)}))

Let me know if this works for you, and I will explain in details on how the expression works.

  • spinaka's avatar
    spinaka
    New Contributor III
    4 years ago

    This is perfect @bojanvelevski
    I was trying with index, map and your expression is better than mine. 🙂

    Would you mind explaining the reduce function used here?