Function reduce() and list of maps

RE: Function reduce() and list of maps

Marco Minoia — Wed, 07 Jun 2023 13:28:05 GMT

Thanks to all!

Yes sure, real case doesn't need reduce to perform this operation... but it is an Appian Online Course Exercise (VOF_AdvExpP2_L2_Ex1_Answer)

It was jut to understand the behavior of reduce() in this particular case.

RE: Function reduce() and list of maps

Peter Lewis — Wed, 07 Jun 2023 12:52:26 GMT

Yeah I can't really think of a scenario where you would use reduce with the sum() function. Stewart is correct, but for sum you don't even need to flatten it - just sum(local!sensor.data) will work too!

RE: Function reduce() and list of maps

Stewart Burchell — Wed, 07 Jun 2023 08:52:25 GMT

The reduce() function loops on the list of lists that you've provided and the fourth list is one item longer than the others (i.e. the value 29). The function can only work correctly on lists that are the same length. To make it work you'll need to add an additional value 0 to all of the lists that are longer thus:

a!localVariables(
  local!sensor: {
    a!map(data: { 125, 92, 22, 63, 73, 28, 19, 0 }),
    a!map(data: { 35, 65, 92, 22, 63, 73, 28, 0 }),
    a!map(data: { 2, 35, 65, 22, 63, 73, 18, 29 }),
    a!map(data: { 9, 35, 65, 63, 35, 28, 19, 0 })
  },
  reduce(fn!sum, 0, local!sensor.data)
)

Alternatively, you can flatten the list and then simply use fn!sum() thus:

a!localVariables(
  local!sensor: {
    a!map(data: { 125, 92, 22, 63, 73, 28, 19 }),
    a!map(data: { 35, 65, 92, 22, 63, 73, 28 }),
    a!map(data: { 2, 35, 65, 22, 63, 73, 18, 29 }),
    a!map(data: { 9, 35, 65, 63, 35, 28, 19 })
  },
  fn!sum(
    a!flatten(local!sensor.data)
  )
)