# Reduce Function

Reduce function is used to do any computation while iterating on an array, computation result is not lost while iteration. it’s a very helpful function where you have to do computation on some array element.

reduce(Array<T>, (item: T, accumulator: T) -> T): T | Null

or

Array<T> reduce( (item: T, accumulator: T) -> T): T | Null

Here

• Array – is the array on which we want to apply reduce function
• Item
• item in the input array
• Refer as \$
• Takes 1st array item value in case acc is defined
• Takes 2nd array item value in case acc is not defined
• Accumulator (acc)
• Store the results of lambda expression after each iteration in reduce function
• Refer as \$\$
• We can explicitly define the initial value like [2,3,3] reduce ((item, acc = “2”) → acc * item)
• If initial value is not defined then it will take the value of first item of array.
• Iteration
• no of item in array minus 1 in case acc is not initialized
• no of item in array in case acc is initialized

Lets see the use case where

acc value is not initialized

Dataweave:

```%dw 2.0
output application/json
---
[2, 3] reduce (\$ + \$\$)
```

Here

• [2,3] – is the input array
• acc -> \$\$ will take the 1st item value = 2 (as acc is not initialized)
• \$ will take the 2nd item value = 3 (as acc is not initialized)
• Loop count = no of item in array minus 1 (as acc is not initialized) = 2 – 1 = 1
• Acc = (\$=3 + \$\$=2) = 5

So result will be 5

acc value is initialized

Dataweave:

```%dw 2.0
output application/json
---
[2,3] reduce ((item, acc = 4) -> acc + item)
```

Here

• [2,3] – is the input array
• acc will take the initialized value = 4
• item will take 1st item value = 2 (as acc is initialized)
• Loop count = no of item in array (as acc is initialized) = 2
• Acc = acc + item -> 4 + 2 -> 6
• Acc = acc + item -> 6 + 3 -> 9

So result will be 9

more details

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View all comments Rizwan
7 months ago

Hello Admin,
while concatenating using reduce function getting the output as “54321”
—-
if acc value is not initialized
acc -> \$\$ will take the 1st item value
\$ will take the 2nd item value

```[1,2,3,4,5] reduce ((item,acc) -> item ++ acc)
```