I have data in CDT where i need to apply some validations to that data

What type of aggregation are you trying to perform? In your example, the name and school always seem to be linked. Can two schools have the same name, and can one school have different names in different rows? Also, is this data already in the Db or do you want o aggregate it in a process model after it is entered by a user?

Hi Bharghavi,

Could you please elaborate your use case bit further? and There are few plugins available for the similar functionality. Please find them in the Shared components and let us know if it meet your requirement.

this data is in process model where user will enter and then again i need to apply aggregation on two columns which have same value, like i need to count as 2 for the set as abc and xyz

Does the user need this grouping displayed immediately back to them? Something like this can be achieved by a view using group by in SQL or the query aggregation functionality in Appian. Be careful though, using group by on large data sets can have performance issues.

What kind of validations are you trying to add - just the fact that there are duplicate values or do you need to specify directly which ones are the duplicates? you can check duplicates by doing something like length(array) <> length(union(array, array)) in which you're comparing the length of the original against the distinct set of values in your list. 

Not an efficient way, but you could also do something like:

a!forEach(
  union(array, array),
  {
    'value': fv!item,
    'count': count(wherecontains(fv!item, array))
  }
)

OOB report builder provides you a easy way to create aggregated report or query

Depending on your situation it might also work to perform the aggregation in a database view and query the count from there.