Create an Array of Numbers in DataWeave

Sometimes we need a simple array to write up/test functionality. In such cases, we create an array, as shown below, and use it.

int[] arr = new int[] {1,2,3,4,5};

But what if we need it in a large size, something like 10,000? In such cases, we create an array with an expected size, and it starts populating data in a simple for/while loop such as below.

int[] arr = new int[10000];
for( int i = 0; i< arr.length; i++ ) {
arr[i] = i+1;
}

The same situation has happened to me in a Transform Message component while I was trying to work on a function that takes an array of numbers as input payload and sends to batch job. To test my batch step performance, I needed a big payload array like 1,000,000. This is how I was able to figure out how to create an array using DataWeave directly. At the same time, I didn't want to go for a Java method just to test my functionality. 

A custom recursive function populates the data until the specified max number.

Here is the code for this.

%dw 2.0 
output application/json
fun prepareList(list:Array, maxSize: Number) = if(sizeOf(list) >= maxSize )
list
else
prepareList(list ++ [(sizeOf(list) + 1) as Number],maxSize)
---
prepareList([],1000)

The output displayed in Transform Message's preview:

[
  1,
  2,
  3,
  4,
  5,
  6,
  7,
  8,
  9,
  10,
.
.
.
  997,
  998,
  999,
  1000
]

Let me know your thoughts in the comments.