Update Array Recursively

Question

Hi,
I am trying to update an array of CDTs recursively.
Base Array : 
{ {name:"Alex",rollNumber:null}, {name:"Stephen",rollNumber:3}, {name:"Dave",rollNumber:4}, {name:"Steave",rollNumber:5}, {name:"Rosey",rollNumber:7}, {name:"John",rollNumber:8}, {name:"Nile",rollNumber:10} }
Now, If I insert number 4  where rollNumber is null , if that number exists in CDT array then all numbers greater than 4 should increase by1 until all duplicates are change to unique number, but all numbers less than 4 should remain unchanged.
This is how numbers should change :
4->5,
5->6
Since there are no duplicates after 6 then increment should stop here,
Updated Array: { {name:"Stephen",rollNumber:3}, {name:"Alex",rollNumber:4}, {name:"Dave",rollNumber:5}, {name:"Steave",rollNumber:6}, {name:"Rosey",rollNumber:7}, {name:"John",rollNumber:8}, {name:"Nile",rollNumber:10} },

Please help me with it

stewart.burchell · Answer

Like a lot of problems, you can break this down into smaller problems to solve.

solve how to take you array and insert ONE new value into it
1. solve inserting a value that doesn't yet exist in the array
2. solve inserting a value that does exist in the array
solve how to invoke the above for a list of values

For 1 you can write an expression rule that takes as its input your array of integers that you want to modify and a single integer that you want to insert into the array.

For 2 there is the reduce() function which you can use to recursively call your new expression.

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