# ECB FX Trend Analyzer & Pair Ranker

### Overview
This R script automates the extraction and statistical analysis of daily foreign exchange rates from the European Central Bank (ECB). Designed for trend-following or long/short strategy research, it identifies the top FX pairs exhibiting the strongest, most predictable linear trends over a customizable rolling window. 

Instead of relying on standard return/volatility metrics, it ranks pairs using a custom **Signal-to-Noise Ratio** derived from linear regression, isolating pairs that move cleanly in one direction with minimal chop.

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### Key Features
* **Automated Data Ingestion:** Securely downloads, unzips, and cleans the latest historical daily exchange rate dataset directly from the ECB repository.
* **Dynamic Cross-Pair Generation:** Automatically calculates non-EUR cross-pairs (e.g., USD/JPY, GBP/JPY) on the fly based on any user-defined list of target currencies.
* **Custom Timeframes:** Allows users to easily slice the dataset to analyze specific lookback periods (e.g., the last 720 days).
* **Statistical Ranking Methodology:** * Runs a simple linear regression for each currency pair (Exchange Rate ~ Time).
  * Extracts the slope (**Beta**) to measure the strength and direction of the trend.
  * Extracts the Residual Standard Error (**RSE**) to measure the volatility or "noise" around that trendline.
  * Ranks all pairs by **|Beta| / RSE**, surfacing the top 3 pairs with the smoothest, most predictable trajectories regardless of whether they are trending up or down.

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### Prerequisites
* **R (Version 3.0 or higher):** The script relies entirely on base R functions. No external libraries (like `dplyr` or `quantmod`) are required.
* **Internet Connection:** Required for the script to automatically fetch the latest dataset directly from the ECB servers.

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### How to Use

**1. Open the Script**
Open the `.R` file in your preferred environment (RStudio, VS Code, or the standard R GUI).

**2. Configure Your Parameters**
At the very top of the script, locate the `CONFIGURATION` section to customize your analysis:
* `target_currencies`: An array of the currency tickers you want to analyze. The script will automatically generate all possible cross-pairs from this list. *(Note: All original columns are priced with a EUR base by default).*
* `n_days_to_analyze`: An integer representing your lookback window in days (e.g., `720` for roughly two years). Set this to `NULL` to analyze the entire historical dataset dating back to 1999.

```R
# Example Configuration
target_currencies <- c("USD", "JPY", "GBP")
n_days_to_analyze <- 720