algorithm/Java
1
0
Fork 0
mirror of https://github.com/TheAlgorithms/Java.git synced 2025-12-19 07:00:35 +08:00
Code Issues Packages Projects Releases Wiki Activity

refactor: Enhance docs, code, add tests in Means (#6750)

Browse Source
This commit is contained in:
Hardik Pawar
2025-10-15 14:44:00 +05:30
committed by GitHub
parent c6497a23ec
commit f8688ba38d
2 changed files with 255 additions and 41 deletions
Download Patch File Download Diff File Expand all files Collapse all files

97
src/main/java/com/thealgorithms/maths/Means.java
View File

@@ -4,9 +4,27 @@ import java.util.stream.StreamSupport;
import org.apache.commons.collections4.IterableUtils;
/**
* https://en.wikipedia.org/wiki/Mean
* Utility class for computing various types of statistical means.
* <p>
* by: Punit Patel
* This class provides static methods to calculate different types of means
* (averages)
* from a collection of numbers. All methods accept any {@link Iterable}
* collection of
* {@link Double} values and return the computed mean as a {@link Double}.
* </p>
*
* <p>
* Supported means:
* <ul>
* <li><b>Arithmetic Mean</b>: The sum of all values divided by the count</li>
* <li><b>Geometric Mean</b>: The nth root of the product of n values</li>
* <li><b>Harmonic Mean</b>: The reciprocal of the arithmetic mean of
* reciprocals</li>
* </ul>
* </p>
*
* @see <a href="https://en.wikipedia.org/wiki/Mean">Mean (Wikipedia)</a>
* @author Punit Patel
*/
public final class Means {
@@ -14,41 +32,90 @@ public final class Means {
}
/**
* @brief computes the [Arithmetic Mean](https://en.wikipedia.org/wiki/Arithmetic_mean) of the input
* @param numbers the input numbers
* @throws IllegalArgumentException empty input
* Computes the arithmetic mean (average) of the given numbers.
* <p>
* The arithmetic mean is calculated as: (x₁ + x₂ + ... + xₙ) / n
* </p>
* <p>
* Example: For numbers [2, 4, 6], the arithmetic mean is (2+4+6)/3 = 4.0
* </p>
*
* @param numbers the input numbers (must not be empty)
* @return the arithmetic mean of the input numbers
* @throws IllegalArgumentException if the input is empty
* @see <a href="https://en.wikipedia.org/wiki/Arithmetic_mean">Arithmetic
* Mean</a>
*/
public static Double arithmetic(final Iterable<Double> numbers) {
checkIfNotEmpty(numbers);
return StreamSupport.stream(numbers.spliterator(), false).reduce((x, y) -> x + y).get() / IterableUtils.size(numbers);
double sum = StreamSupport.stream(numbers.spliterator(), false).reduce(0d, (x, y) -> x + y);
int size = IterableUtils.size(numbers);
return sum / size;
}
/**
* @brief computes the [Geometric Mean](https://en.wikipedia.org/wiki/Geometric_mean) of the input
* @param numbers the input numbers
* @throws IllegalArgumentException empty input
* Computes the geometric mean of the given numbers.
* <p>
* The geometric mean is calculated as: ⁿ√(x₁ × x₂ × ... × xₙ)
* </p>
* <p>
* Example: For numbers [2, 8], the geometric mean is √(2×8) = √16 = 4.0
* </p>
* <p>
* Note: This method may produce unexpected results for negative numbers,
* as it computes the real-valued nth root which may not exist for negative
* products.
* </p>
*
* @param numbers the input numbers (must not be empty)
* @return the geometric mean of the input numbers
* @throws IllegalArgumentException if the input is empty
* @see <a href="https://en.wikipedia.org/wiki/Geometric_mean">Geometric
* Mean</a>
*/
public static Double geometric(final Iterable<Double> numbers) {
checkIfNotEmpty(numbers);
return Math.pow(StreamSupport.stream(numbers.spliterator(), false).reduce((x, y) -> x * y).get(), 1d / IterableUtils.size(numbers));
double product = StreamSupport.stream(numbers.spliterator(), false).reduce(1d, (x, y) -> x * y);
int size = IterableUtils.size(numbers);
return Math.pow(product, 1.0 / size);
}
/**
* @brief computes the [Harmonic Mean](https://en.wikipedia.org/wiki/Harmonic_mean) of the input
* @param numbers the input numbers
* @throws IllegalArgumentException empty input
* Computes the harmonic mean of the given numbers.
* <p>
* The harmonic mean is calculated as: n / (1/x₁ + 1/x₂ + ... + 1/xₙ)
* </p>
* <p>
* Example: For numbers [1, 2, 4], the harmonic mean is 3/(1/1 + 1/2 + 1/4) =
* 3/1.75 ≈ 1.714
* </p>
* <p>
* Note: This method will produce unexpected results if any input number is
* zero,
* as it involves computing reciprocals.
* </p>
*
* @param numbers the input numbers (must not be empty)
* @return the harmonic mean of the input numbers
* @throws IllegalArgumentException if the input is empty
* @see <a href="https://en.wikipedia.org/wiki/Harmonic_mean">Harmonic Mean</a>
*/
public static Double harmonic(final Iterable<Double> numbers) {
checkIfNotEmpty(numbers);
return IterableUtils.size(numbers) / StreamSupport.stream(numbers.spliterator(), false).reduce(0d, (x, y) -> x + 1d / y);
double sumOfReciprocals = StreamSupport.stream(numbers.spliterator(), false).reduce(0d, (x, y) -> x + 1d / y);
int size = IterableUtils.size(numbers);
return size / sumOfReciprocals;
}
/**
* Validates that the input iterable is not empty.
*
* @param numbers the input numbers to validate
* @throws IllegalArgumentException if the input is empty
*/
private static void checkIfNotEmpty(final Iterable<Double> numbers) {
if (!numbers.iterator().hasNext()) {
throw new IllegalArgumentException("Emtpy list given for Mean computation.");
throw new IllegalArgumentException("Empty list given for Mean computation.");
}
}
}