From c7433926c5122f639a90fa646b661531640ac064 Mon Sep 17 00:00:00 2001
From: Sam Millington <s.j.millington@hotmail.co.uk>
Date: Fri, 26 Jul 2019 05:18:20 +0100
Subject: [PATCH] [BAEL-2951] - Sorting a string that may contain a number code
 (#7388)

---
 .../NaturalOrderComparators.java              | 30 +++++++
 .../NaturalOrderComparatorsUnitTest.java      | 79 +++++++++++++++++++
 2 files changed, 109 insertions(+)
 create mode 100644 algorithms-miscellaneous-3/src/main/java/com/baeldung/algorithms/stringsortingbynumber/NaturalOrderComparators.java
 create mode 100644 algorithms-miscellaneous-3/src/test/java/com/baeldung/algorithms/stringsortingbynumber/NaturalOrderComparatorsUnitTest.java

diff --git a/algorithms-miscellaneous-3/src/main/java/com/baeldung/algorithms/stringsortingbynumber/NaturalOrderComparators.java b/algorithms-miscellaneous-3/src/main/java/com/baeldung/algorithms/stringsortingbynumber/NaturalOrderComparators.java
new file mode 100644
index 0000000000..376b196aa1
--- /dev/null
+++ b/algorithms-miscellaneous-3/src/main/java/com/baeldung/algorithms/stringsortingbynumber/NaturalOrderComparators.java
@@ -0,0 +1,30 @@
+package com.baeldung.algorithms.stringsortingbynumber;
+
+import java.util.Comparator;
+
+public final class NaturalOrderComparators {
+
+    private static final String DIGIT_AND_DECIMAL_REGEX = "[^\\d.]";
+
+    private NaturalOrderComparators() {
+        throw new AssertionError("Let's keep this static");
+    }
+
+    public static Comparator<String> createNaturalOrderRegexComparator() {
+        return Comparator.comparingDouble(NaturalOrderComparators::parseStringToNumber);
+    }
+
+    private static double parseStringToNumber(String input){
+
+        final String digitsOnly = input.replaceAll(DIGIT_AND_DECIMAL_REGEX, "");
+
+        if("".equals(digitsOnly)) return 0;
+
+        try{
+            return Double.parseDouble(digitsOnly);
+        }catch (NumberFormatException nfe){
+            return 0;
+        }
+    }
+
+}
diff --git a/algorithms-miscellaneous-3/src/test/java/com/baeldung/algorithms/stringsortingbynumber/NaturalOrderComparatorsUnitTest.java b/algorithms-miscellaneous-3/src/test/java/com/baeldung/algorithms/stringsortingbynumber/NaturalOrderComparatorsUnitTest.java
new file mode 100644
index 0000000000..549151bc93
--- /dev/null
+++ b/algorithms-miscellaneous-3/src/test/java/com/baeldung/algorithms/stringsortingbynumber/NaturalOrderComparatorsUnitTest.java
@@ -0,0 +1,79 @@
+package com.baeldung.algorithms.stringsortingbynumber;
+
+import com.baeldung.algorithms.stringsortingbynumber.NaturalOrderComparators;
+import org.junit.Test;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+
+import static org.junit.Assert.*;
+
+public class NaturalOrderComparatorsUnitTest {
+
+    @Test
+    public void givenSimpleStringsContainingIntsAndDoubles_whenSortedByRegex_checkSortingCorrect() {
+
+        List<String> testStrings = Arrays.asList("a1", "b3", "c4", "d2.2", "d2.4", "d2.3d");
+
+        testStrings.sort(NaturalOrderComparators.createNaturalOrderRegexComparator());
+
+        List<String> expected = Arrays.asList("a1", "d2.2", "d2.3d", "d2.4", "b3", "c4");
+
+        assertEquals(expected, testStrings);
+
+
+    }
+
+    @Test
+    public void givenSimpleStringsContainingIntsAndDoublesWithAnInvalidNumber_whenSortedByRegex_checkSortingCorrect() {
+
+        List<String> testStrings = Arrays.asList("a1", "b3", "c4", "d2.2", "d2.4", "d2.3.3d");
+
+        testStrings.sort(NaturalOrderComparators.createNaturalOrderRegexComparator());
+
+        List<String> expected = Arrays.asList("d2.3.3d", "a1", "d2.2", "d2.4", "b3", "c4");
+
+        assertEquals(expected, testStrings);
+
+
+    }
+
+    @Test
+    public void givenAllForseenProblems_whenSortedByRegex_checkSortingCorrect() {
+
+        List<String> testStrings = Arrays.asList("a1", "b3", "c4", "d2.2", "d2.f4", "d2.3.3d");
+
+        testStrings.sort(NaturalOrderComparators.createNaturalOrderRegexComparator());
+
+        List<String> expected = Arrays.asList("d2.3.3d", "a1", "d2.2", "d2.f4", "b3", "c4");
+
+        assertEquals(expected, testStrings);
+
+
+    }
+
+    @Test
+    public void givenComplexStringsContainingSeparatedNumbers_whenSortedByRegex_checkNumbersCondensedAndSorted() {
+
+        List<String> testStrings = Arrays.asList("a1b2c5", "b3ght3.2", "something65.thensomething5"); //125, 33.2, 65.5
+
+        List<String> expected = Arrays.asList("b3ght3.2", "something65.thensomething5", "a1b2c5" );
+
+        testStrings.sort(NaturalOrderComparators.createNaturalOrderRegexComparator());
+
+        assertEquals(expected, testStrings);
+
+    }
+
+    @Test
+    public void givenStringsNotContainingNumbers_whenSortedByRegex_checkOrderNotChanged() {
+
+        List<String> testStrings = Arrays.asList("a", "c", "d", "e");
+        List<String> expected = new ArrayList<>(testStrings);
+
+        testStrings.sort(NaturalOrderComparators.createNaturalOrderRegexComparator());
+
+        assertEquals(expected, testStrings);
+    }
+}
\ No newline at end of file