How to remove duplicate index form local(Array)

Hi ,

You can use union function to get distinct values .
union(local!voucherDetails,local!voucherDetails)

I have tried to replicate your use, plz refer this.

a!localVariables(
  local!test: {
    {
      username: "",
      buduget: 2023,
      dept: 123456789
    },
    {
      username: "",
      buduget: 2023,
      dept: 123456789
    },
    {
      username: "Rishikesh",
      buduget: 2023,
      dept: 123
    },
    {
      username: "Rishikesh",
      buduget: 2023,
      dept: 123
    },
    {
      username: "Rishikesh",
      buduget: 2023,
      dept: 123
    }
  },
  union(local!test, local!test)
)

How to keep only unique based on the dept value? 

you can use the union function, it compares all the fields.