**Other posts from this series:**

__DataWeave programming challenge #1: Add numbers separated by paragraphs and get the max number____DataWeave programming challenge #2: Rock Paper Scissors game score system____DataWeave programming challenge #3: Count palindrome phrases using the Strings module____DataWeave programming challenge #4: Solve the Tower of Hanoi mathematical puzzle____DataWeave programming challenge #5: Reverse a phrase's words, but keep the punctuation____DataWeave programming challenge #6: Using tail-recursion to get the factorial of a number____DataWeave programming challenge #7: Modify certain values from a JSON structure__**DataWeave programming challenge #8: Sum all digits to get a 1-digit number**

**In this post:**

Try to solve this challenge on your own to maximize learning. We recommend you refer to the __DataWeave documentation____ __** only**. Try to avoid using Google or asking others so you can learn on your own and become a DataWeave expert!

## Input

Consider the following input payload (can be of **txt** format):

```
2456
2
25235
2456
6
54
58795
3
456
76544
0
```

## Explanation of the problem

Create a DataWeave script to sum all the digits from the input payload until there's only one digit left.

For example,

123 + 456 = 579

579 is broken down into 5 + 7 + 9 = 21

21 is broken down into 2 + 1 = 3

The final result is 3 because it's a 1-digit number

## Expected output

In this case, the expected output would be:

`2`

## Clues

If you're stuck with your solution, feel free to check out some of these clues to give you ideas on how to solve it!

## Answer

If you haven't solved this challenge yet, we encourage you to keep trying! It's ok if it's taking longer than you thought. We all have to start somewhere âœ¨ Check out the clues and read the docs before giving up. You got this!! ðŸ’™

There are many ways to solve this challenge, but you can find some solutions we provide here so you can compare your result with us.

Feel free to comment your code below for others to see! ðŸ˜„

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@armandomejiam

As per your code, the expected output should be 9, but got 0

%dw 2.0 output application/json fun solve(x) = if (sizeOf(x)==1) x else solve((x reduce ((item, accumulator ) -> accumulator + item))) --- solve(payload splitBy('\n'))

after I viewed the simple reduce solution provided by Diksha, I updated my gist to add a "recursive reduce" function. Also, after realizing the "mod 9" solution (thanks Sai Teja) I wrote this simplistic solution: %dw 2.0 import lines from dw::core::Strings output application/json --- (lines(payload) joinBy "") as Number mod 9

output application/json fun singleit(L:Array):Number=singleit(sum(L map singleit($ as Number default $))) fun singleit(X:Null):Number =0 fun singleit(N: Number):Number = if (N==0) 0 else do{var res = (N mod 9) --- if(res==0) 9 else res} fun singleit(Str :Any) : Number =0 --- singleit(payload splitBy "\n")

%dw 2.0 output application/json import lines from dw::core::Strings fun reduceToOneDigit(inputValue) = inputValue match { case d if(d is Number and sizeOf(d) == 1) -> d else -> reduceToOneDigit($ reduce $$ + $) } --- reduceToOneDigit(lines(payload))