Extracting number from string

Author: yadavan88

core-kotlin-modules/core-kotlin-strings-5/README.md

@@ -0,0 +1,6 @@
+## Core Kotlin Strings
+
+This module contains articles about core Kotlin strings.
+
+### Relevant Articles
+

core-kotlin-modules/core-kotlin-strings-5/pom.xml

@@ -0,0 +1,25 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+    <artifactId>core-kotlin-strings-5</artifactId>
+    <name>core-kotlin-strings-5</name>
+    <packaging>jar</packaging>
+
+    <parent>
+        <groupId>com.baeldung</groupId>
+        <artifactId>core-kotlin-modules</artifactId>
+        <version>1.0.0-SNAPSHOT</version>
+    </parent>
+
+    <dependencies>
+        <dependency>
+            <groupId>org.junit.jupiter</groupId>
+            <artifactId>junit-jupiter-params</artifactId>
+            <version>5.10.2</version>
+            <scope>test</scope>
+        </dependency>
+    </dependencies>
+
+</project>

core-kotlin-modules/core-kotlin-strings-5/src/test/kotlin/com/baeldung/extractnumber/NumberExtractUnitTest.kt

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+package com.baeldung.extractnumber
+
+import org.junit.jupiter.api.Assertions
+import org.junit.jupiter.params.ParameterizedTest
+import org.junit.jupiter.params.provider.CsvSource
+
+fun extractUsingRegex(str: String): Long? {
+    return Regex("\\d+").find(str)?.value?.toLongOrNull()
+}
+
+fun extractMultipleUsingRegex(str: String): List<Long> {
+    return Regex("\\d+").findAll(str).map { it.value.toLong() }.toList()
+}
+
+fun extractNumbersUsingSplitAndRegex(str: String): List<Long> {
+    return str.split(Regex("\\D+"))
+        .filter { it.isNotBlank() }
+        .map { it.toLong() }
+}
+
+fun extractNumbersUsingLoop(str: String): List<Long> {
+    val numbers = mutableListOf<Long>()
+    val currentNumber = StringBuilder()
+
+    for (char in str) {
+        if (char.isDigit()) {
+            currentNumber.append(char)
+        } else if (currentNumber.isNotEmpty()) {
+            numbers.add(currentNumber.toString().toLong())
+            currentNumber.clear()
+        }
+    }
+
+    if (currentNumber.isNotEmpty()) {
+        numbers.add(currentNumber.toString().toLong())
+    }
+
+    return numbers
+}
+
+
+class NumberExtractUnitTest {
+
+    @ParameterizedTest
+    @CsvSource(
+        "string with 123 and 333 in the text, 123",
+        "another string with 456 and 789, 456",
+        "string 123-234, 123",
+        "no numbers,",
+    )
+    fun `extract first occurrence of number from string using regex`(str: String, expected: String?) {
+        val number = extractUsingRegex(str)
+        Assertions.assertEquals(number, expected?.toLongOrNull())
+    }
+
+    @ParameterizedTest
+    @CsvSource(
+        "string with 123 and 333 in the text, 123:333",
+        "another string with 456 and 789, 456:789",
+        "string 123-234, 123:234",
+        "no numbers,",
+    )
+    fun `extract all occurrences of numbers from string using regex`(str: String, expected: String?) {
+        val numbers = extractMultipleUsingRegex(str)
+        val expectedList = expected?.split(":")?.map { it.toLong() } ?: emptyList()
+        Assertions.assertEquals(expectedList, numbers)
+    }
+
+    @ParameterizedTest
+    @CsvSource(
+        "string with 123 and 333 in the text, 123:333",
+        "another string with 456 and 789, 456:789",
+        "string 123-234, 123:234",
+        "no numbers,",
+    )
+    fun `extract all occurrences of numbers from string using split and regex`(str: String, expected: String?) {
+        val numbers = extractNumbersUsingSplitAndRegex(str)
+        val expectedList = expected?.split(":")?.map { it.toLong() } ?: emptyList()
+        Assertions.assertEquals(expectedList, numbers)
+    }
+
+    @ParameterizedTest
+    @CsvSource(
+        "string with 123 and 333 in the text, 123:333",
+        "another string with 456 and 789, 456:789",
+        "string 123-234, 123:234",
+        "no numbers,",
+    )
+    fun `extract all occurrences of numbers from string using loop`(str: String, expected: String?) {
+        val numbers = extractNumbersUsingLoop(str)
+        val expectedList = expected?.split(":")?.map { it.toLong() } ?: emptyList()
+        Assertions.assertEquals(expectedList, numbers)
+    }
+
+}

core-kotlin-modules/pom.xml

@@ -64,6 +64,7 @@
         <module>core-kotlin-strings-2</module>
         <module>core-kotlin-strings-3</module>
         <module>core-kotlin-strings-4</module>
+        <module>core-kotlin-strings-5</module>
         <module>core-kotlin-string-conversions</module>
         <module>core-kotlin-files</module>
         <module>core-kotlin-operators</module>