From a3560d69423e086ab2f296b0163172a1286ceed4 Mon Sep 17 00:00:00 2001
From: Ryuu Mitsuki <dhefam31@gmail.com>
Date: Fri, 13 Sep 2024 15:36:39 +0700
Subject: [PATCH] feat: Add support for negative indices in `display` methods

* Enhanced the `display(int index)` method in the `Matrix` class to support negative indices. Negative indices are now interpreted as counting from the end of the matrix. For instance, an index of `-1` refers to the last row, `-2` refers to the second-to-last row, and so on.
* Adjusted the index calculation to convert negative indices into valid positive indices.
* Added checks to ensure that the adjusted index is within valid bounds for the matrix rows.
* Improved error handling to raise an `InvalidIndexException` with a clear message if the adjusted index is out of bounds.
* Updated the static `display(double[][] arr, int index)` method to support negative indices similarly.

These updates provide greater flexibility for accessing rows in matrices and 2D arrays using negative indices, aligning with common conventions and improving usability.
---
 src/main/java/com/mitsuki/jmatrix/Matrix.java | 52 ++++++++-----------
 1 file changed, 22 insertions(+), 30 deletions(-)

diff --git a/src/main/java/com/mitsuki/jmatrix/Matrix.java b/src/main/java/com/mitsuki/jmatrix/Matrix.java
index 8b18266..62d076f 100644
--- a/src/main/java/com/mitsuki/jmatrix/Matrix.java
+++ b/src/main/java/com/mitsuki/jmatrix/Matrix.java
@@ -5237,25 +5237,20 @@ final public void display() {
      * @see                           #getEntries()
      */
     final public void display(int index) {
-        if (this.ENTRIES != null) {
-            // Check for negative index and throw the exception
-            if (index < 0) {
-                cause = new InvalidIndexException(
-                    "Invalid given index. Index cannot be a negative value.");
-            }
-            // Check if the given index greater than number of rows this matrix
-            else if (index > this.ROWS - 1) {
-                cause = new InvalidIndexException(
-                    "Invalid given index. Index cannot be larger than number of rows.");
-            }
-
-            // Throw the exception if got one
-            if (cause != null) raise(cause);
-
-            System.out.println(Arrays.toString(this.ENTRIES[index]));
-        } else {
+        if (this.ENTRIES == null) {
             System.out.println("<null_matrix>");
+            return;
+        }
+
+        int rows = this.getNumRows();
+        index += (index < 0) ? rows: 0;  // Support negative index
+        if (index < 0 || index >= rows) {
+            raise(new InvalidIndexException("Given row index is out of bounds: " +
+                ((index < 0) ? (index - rows) : index)
+            ));
         }
+
+        System.out.println(Arrays.toString(this.ENTRIES[index]));
     }
 
 
@@ -5312,21 +5307,18 @@ final public static void display(double[ ][ ] arr) {
     final public static void display(double[ ][ ] arr, int index) {
         if (arr == null || arr.length == 0) {
             System.out.println("<null_2darray>");
-        } else {
-            // Checking index value
-            if (index < 0) {
-                cause = new InvalidIndexException(
-                    "Invalid given index. Index cannot be a negative value.");
-            } else if (index > arr.length - 1) {
-                cause = new InvalidIndexException(
-                    "Invalid given index. Index cannot be larger than number of rows.");
-            }
-
-            // Throw the exception if got one
-            if (cause != null) raise(cause);
+            return;
+        }
 
-            System.out.println(Arrays.toString(arr[index]));
+        int rows = arr.length;
+        index += (index < 0) ? rows: 0;  // Support negative index
+        if (index < 0 || index >= rows) {
+            raise(new InvalidIndexException("Given row index is out of bounds: " +
+                ((index < 0) ? (index - rows) : index)
+            ));
         }
+
+        System.out.println(Arrays.toString(arr[index]));
     }