# DataWeave programming challenge #7: Modify certain values from a JSON structure > Create a DataWeave script that will update all the values to uppercase, except the ones in which the field equals thisname. - **Author:** Alex Martinez - **Published:** Jun 13, 2023 - **Category:** Challenges - **Tags:** MuleSoft, DataWeave - **Source:** https://prostdev.com/post/dataweave-programming-challenge-7 --- ## Series: DataWeave Programming Challenges (Part 7 of 8) 1. [DataWeave programming challenge #1: Add numbers separated by paragraphs and get the max number](https://prostdev.com/post/dataweave-programming-challenge-1) 2. [DataWeave programming challenge #2: Rock Paper Scissors game score system](https://prostdev.com/post/dataweave-programming-challenge-2) 3. [DataWeave programming challenge #3: Count palindrome phrases using the Strings module](https://prostdev.com/post/dataweave-programming-challenge-3) 4. [DataWeave programming challenge #4: Solve the Tower of Hanoi mathematical puzzle](https://prostdev.com/post/dataweave-programming-challenge-4) 5. [DataWeave programming challenge #5: Reverse a phrase's words, but keep the punctuation](https://prostdev.com/post/dataweave-programming-challenge-5) 6. [DataWeave programming challenge #6: Using tail-recursion to get the factorial of a number](https://prostdev.com/post/dataweave-programming-challenge-6) 7. DataWeave programming challenge #7: Modify certain values from a JSON structure (this post) 8. [DataWeave programming challenge #8: Sum all digits to get a 1-digit number](https://prostdev.com/post/dataweave-programming-challenge-8) --- Try to solve this challenge on your own to maximize learning. We recommend you refer to the [DataWeave documentation](https://docs.mulesoft.com/dataweave/latest/) **only**. Try to avoid using Google or asking others so you can learn on your own and become a DataWeave expert! > [!PLAYGROUND] > [Solve on the Playground](https://dataweave.mulesoft.com/learn/playground?projectMethod=GHRepo&repo=alexandramartinez%2Fdataweave-challenges&path=challenges%2F7) > [!TIP] > Instead of trying to write the whole code yourself, browse in the documentation for any function that would do the work for you 👀 ## Input Consider the following JSON input payload: ``` { "name": "a", "object": { "name": "b", "l": [ { "other": "c", "list": [ ] }, { "thisname": "def", "list": [ { "this": "500e", "l": [ { "finalname": "f" }, { "finalname": "ghijk" } ] } ] } ] }, "array": [ { "thisname": "h" }, { "xyz": "abc123" } ] } ``` ## Explanation of the problem Create a DataWeave script that will update all the values to uppercase, **except** the ones in which the field equals **thisname**. For example, the first field **name** with the value **"a"** has to be transformed to **"A"**. However, the field **thisname** with the value of **"def"** should stay the same. ## Expected output In this case, the expected output would be: ``` { "name": "A", "object": { "name": "B", "l": [ { "other": "C", "list": [ ] }, { "thisname": "def", "list": [ { "this": "500E", "l": [ { "finalname": "F" }, { "finalname": "GHIJK" } ] } ] } ] }, "array": [ { "thisname": "h" }, { "xyz": "ABC123" } ] } ``` ## 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! ### Clue #1 Check out the [Tree](https://docs.mulesoft.com/dataweave/latest/dw-tree) module to see if any of those functions is useful for this case. ### Clue #2 Check out the [mapLeafValues](https://docs.mulesoft.com/dataweave/latest/dw-tree-functions-mapleafvalues) function. ### Clue #3 Use the [upper](https://docs.mulesoft.com/dataweave/latest/dw-core-functions-upper) function to transform the strings to uppercase. ### Clue #4 Use **path[-1].selector** to retrieve the name of each value's field and compare it with a given string value. ## 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 ✨ Check out the clues and read the docs before giving up. You got this!! 💙 There are many ways to solve this challenge, but you can find here some solutions we are providing so you can compare your result with us. ### Solution #1 ```dataweave %dw 2.0 import mapLeafValues from dw::util::Tree output application/json --- payload mapLeafValues ((value, path) -> if (path[-1].selector == "thisname") value else upper(value) ) ``` ### Solution #2 ```dataweave %dw 2.0 import mapLeafValues from dw::util::Tree output application/json --- payload mapLeafValues if ($$[-1].selector == "thisname") $ else upper($) ``` Subscribe to receive notifications as soon as new content is published ✨ --- ## Reader notes **Sudiptaa** (Jun 13, 2023): Used tree: ```dataweave %dw 2.0 output application/json import * from dw::util::Tree --- payload mapLeafValues ((value, path) -> if(path.selector contains 'thisname') value else upper(value) ) ``` **Kenneth Brennan** (Jun 13, 2023): I went with a recursive solution: ```dataweave %dw 2.0 output application/json fun capitalizeObject(item: Object) = do{ fun matchItem(item) = item match{ case item is Object -> item mapObject ((value, key, index) -> if(key as String == 'thisname') {(key): value} else {(key): matchItem(value)}) case item is Array -> item map ((item, index) -> matchItem(item)) case item is String -> upper(item) } --- matchItem(item) } --- capitalizeObject(payload) ``` ↳ Reply to Kenneth Brennan — **Alex Martinez** (Jun 13, 2023): I love love love that you're using the `do` keyword to create a local context. This function's structure can be used for any number of modifications in a recursive way. I love it! The only downside being that if there are more than 255 fields (or recursive calls), you will reach the StackOverflow error. But if it's a small payload like this one, you're all good! Thanks for sharing :D ↳ Reply to Alex Martinez — **Kenneth Brennan** (Jun 13, 2023): That pesky stack overflow, I'm not sure how to rewrite this in the same format using tail recursion and match, hard to conceptualize. Might give it another go when I get some free time. Thanks for posting these challenges, I enjoyed this one! **Shyam Raj Prasad** (Jun 13, 2023): My solution is similar to yours with extra type check of string. ```dataweave %dw 2.0 output application/json import * from dw::util::Tree --- payload mapLeafValues ((value, path) -> if(!(path[-1].selector == "thisname") and value is String) upper(value) else value ) ``` --- ## FAQs ### What is the goal of DataWeave programming challenge #7? The challenge is to create a DataWeave script that updates all the values in a JSON structure to uppercase, except the ones whose field equals `thisname`. For example, the field `name` with value "a" becomes "A", but the field `thisname` with value "def" stays the same. ### Which DataWeave function does this challenge use to walk the JSON structure? It uses the `mapLeafValues` function from the `dw::util::Tree` module, which lets you transform each leaf value in the structure. Both provided solutions import `mapLeafValues from dw::util::Tree` and call it on the payload. ### How do I skip the `thisname` field while uppercasing everything else? Inside `mapLeafValues`, you check the field name of each value with `path[-1].selector` and compare it to the string `"thisname"`; if it matches you return the value unchanged, otherwise you apply the `upper` function to convert it to uppercase. ### What does `path[-1].selector` do in the solution? As described in Clue #4, `path[-1].selector` retrieves the name of each value's field so you can compare it with a given string value, which is how the script decides whether a value belongs to the `thisname` field and should be left alone. ### What's the difference between the two provided solutions? Solution #1 uses the explicit lambda form `mapLeafValues ((value, path) -> ...)` and references the field name with `path[-1].selector`, while Solution #2 uses the shorthand anonymous-parameter form, referencing the value with `$` and the field name with `$$[-1].selector`; both produce the same result.