Trouble updating array with information from another array

without the actual values I am finding it hard to debug this code, But I would have tried using displayValue function. also your  

https://docs.appian.com/suite/help/24.3/fnc_conversion_displayvalue.html

Thank you, I will take a look at that.

Sure let me know if you able to achieve desired result. Also in your first approach, your 2 foreach items would be confusing each other. Use the local variables to refer the top level foreach 

Your a!save() call is wrong. You cannot assign a value inside the value attribute of a!save, like you try in line 3. I suggest to check the correct syntax for a!save().

I got it to work but wonder if there is a better way to  write it.  I tried writing the updates all within curly braces, but that doesn't work.  It only updates one of them.  Can you take a look and suggest changes.

a!save(
              local!newEstimates2,
              a!forEach(
                items: local!newEstimates,
                expression: if(
                  a!isNullOrEmpty(
                    wherecontains(
                      fv!item.costAdjustments.contractPeriodNum,
                      tointeger(local!uniqueContractPeriods.period)
                    )
                  ),
                  fv!item,
                  a!update(
                    fv!item,
                    "costAdjustments",
                    a!update(
                      a!update(
                        a!update(
                          a!update(
                            fv!item.costAdjustments,
                            "lengthOfMonth",
                            cast(
                              1,
                              index(
                                local!uniqueContractPeriods.noOfMonths,
                                wherecontains(
                                  fv!item.costAdjustments.contractPeriodNum,
                                  tointeger(local!uniqueContractPeriods.period)
                                ),
                                null
                              )
                            )
                          ),
                          "periodStartDate",
                          index(
                            local!uniqueContractPeriods.startDate,
                            wherecontains(
                              fv!item.costAdjustments.contractPeriodNum,
                              tointeger(local!uniqueContractPeriods.period)
                            ),
                            null
                          )
                        ),
                        "periodEndDate",
                        index(
                          local!uniqueContractPeriods.endDate,
                          wherecontains(
                            fv!item.costAdjustments.contractPeriodNum,
                            tointeger(local!uniqueContractPeriods.period)
                          ),
                          null
                        )
                      ),
                      "LengthOfDay",
                      index(
                        local!uniqueContractPeriods.noOfDays,
                        wherecontains(
                          fv!item.costAdjustments.contractPeriodNum,
                          tointeger(local!uniqueContractPeriods.period)
                        ),
                        null
                      )
                    )
                  )
                )
              )
            )

To resolve such issues, I try to simplify what I am doing. Create a separate expression with some local test data. Then try to understand how to use a!update. Then apply that new knowledge to your actual problem.

This is how I learned to code 40 years ago, and this is how I solve my problems in my last 15 years with Appian.

Stefan,  Thanks you so much.  I still feel new at Appian development.  I wish I had more development time.  I am the only developer and sometimes I have questions.  But I really appreciate you taking time to help.