applyx

Create a fully-functional mini-app called 'DataProcessor' using the Python package 'applyx'. This app should serve as a powerful tool for data scientists and analysts who need to preprocess large datasets efficiently. Your task is to design and implement a user-friendly command-line interface that allows users to perform various data preprocessing tasks such as filtering, transforming, and aggregating data from CSV files.

The core functionalities of your app should include:
- Loading data from a CSV file into a DataFrame
- Filtering rows based on specified conditions
- Applying transformations to specific columns (e.g., converting string representations of numbers to actual numeric types)
- Aggregating data based on one or more columns (e.g., summing values in a column grouped by another column)
- Saving the processed DataFrame back to a CSV file

To achieve these functionalities, you will extensively use the 'applyx' package, which provides high-performance operations on DataFrames. Specifically, you should leverage 'applyx' for applying transformations and aggregations across large datasets without compromising performance. Your implementation should demonstrate how 'applyx' simplifies complex data manipulation tasks, making it easier for users to handle big data efficiently.

Additionally, consider adding advanced features like:
- Support for multiple input/output formats (e.g., JSON, Excel)
- Handling missing data through imputation techniques
- Providing visual feedback or summaries of the data before and after processing

Ensure that your code is well-documented, modular, and includes unit tests to verify its correctness. The final deliverable should consist of a README file explaining how to install and run the application, along with sample data and instructions on how to reproduce the results.