Create mentoring.md

tracks/typescript/exercises/etl/etl/mentoring.md

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+# Mentoring
+
+## ETL
+
+### Problem asks
+
+Restructure grouped letters by point values into individual mappings. 
+Transform the old format (point-value groups) into a new format (letter-score pairs) in TypeScript. 
+Associate lowercase letters with their corresponding point values, transitioning from grouped data to individual letter scoring.
+
+## Reasonable Solution
+
+The code snippet provided in TypeScript represents a function named `transform`. 
+This function takes in an object `oldData`, which has keys representing point values (as strings) and values as arrays of strings (letters associated with those point values).
+
+The function iterates through the `oldData` object, assigning each letter (converted to lowercase) to its corresponding score in the `newData` object. 
+The return value of the function is an object where keys are lowercase letters and values are the associated point values (as numbers).
+
+```typescript
+export function transform(oldData: { [key: string]: string[] }): { [key: string]: number } {
+    const newData: { [key: string]: number } = {};
+
+    for (const [score, letters] of Object.entries(oldData)) {
+        letters.forEach((letter: string) => {
+            newData[letter.toLowerCase()] = parseInt(score);
+        });
+    }
+
+    return newData;
+}
+```
+
+
+### Common Suggestions:
+
+1. **Type Annotations:**
+   - Encourage the use of explicit type annotations for parameters and return values to enhance code readability and maintainability.
+
+   ```typescript
+   export function transform(oldData: { [key: string]: string[] }): { [key: string]: number } {
+   ```
+
+2. **Data Validation:**
+   - Discuss potential edge cases or invalid data scenarios. What happens if the input data is malformed or if a letter is associated with multiple scores?
+
+### Talking Points:
+
+- **ETL Concept:**
+  - Briefly explain the ETL concept, emphasizing its role in transforming data from one format to another.
+
+- **Type Safety:**
+  - Emphasize the use of TypeScript for type safety. Ensure that the input and output types are clearly defined to catch potential runtime errors.
+
+- **Functional Approach:**
+  - Introduce a more functional approach using methods like `map` and `reduce` for constructing the new data object, making the code more concise.
+