appian and maps

Question

Hello,
I am trying to represent the following structure using maps in Appian (for those familiar with C# or Java ... something equivalent to Dictionary<int, List<Object>):
So the list looks something like this:
{ {    taskId: 100,    dependsOnTaskId: 101  }, {    taskId: 100,    dependsOnTaskId: 121 },
 {    taskId: 101,    dependsOnTaskId: 123 },
 {    taskId: 103,    dependsOnTaskId: 0 },
 {    taskId: 123,    dependsOnTaskId: 5 }, }
A task Id might have none or multiple unique dependencies (there are many other constrains but at this point I will just focus on the most basic structure)
After processing this list, I would like to have a map as follows:
{
{
taskId :100 dependencies: 101, 121
},

{
taskId :101 dependencies: 123
},

{
taskId :103 dependencies:
},

{
taskId :123 dependencies: 5
}
}

I am able to build this structure in a process model using a loop but performance seems to be an issue here since the node that calls the expression rule and then builds the map takes more than a minute to process a list with less than a hundred items. Moreover, there is the activity chaining...  I often hit the maximum limit of chains(I know this is a configuration parameters and could potentially be increased, but since the list will be constantly growing, I don't think that is the ideal solution).
The thing is that moving the execution to an expression rule and using a for loop doesn't work: on each iteration, the for loop doesn't take into account any changes made on the previous iteration. Therefore, the result is a flat list of maps with the same structure as the initial list (tasks are not being grouped). I was hoping there will be a way to pass parameters "by reference" but this seems to be a foreign concept in Appian (except in process models I know).
Any advice /help would be greatly appreciated!

Thank you

stewart.burchell · Answer

Hi - this seems to work:a!localVariables(  local!sourceData: {    a!map(taskId: 100, dependsOnTaskId: 101),    a!map(taskId: 100, dependsOnTaskId: 121),    a!map(taskId: 101, dependsOnTaskId: 123),    a!map(taskId: 103, dependsOnTaskId: 0),    a!map(taskId: 123, dependsOnTaskId: 5)  },  local!result: a!forEach(    items: local!sourceData.taskId,    expression: a!map(      taskId: fv!item,      dependencies: local!sourceData.dependsOnTaskId[wherecontains(fv!item, local!sourceData.taskId)]    )  ),  fn!union(local!result,local!result))...with output of:I did notice that your expected output value for 'dependancies' for taskId 103 is blank, whereas your source data has a value of 0. I am assuming you wanted 0. If not then you'll have to add a specific clause to output 'null' when the actual value is 0.If you want an explanation as to what's going on  I'm happy to provide you with one.

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