- add average #20

Author: brunovinicius

src/main/java/br/com/zbra/androidlinq/AbstractStream.java

@@ -5,6 +5,7 @@
 import br.com.zbra.androidlinq.exception.MultipleElementsFoundException;
 
 import java.math.BigDecimal;
+import java.math.MathContext;
 import java.util.*;
 
 abstract class AbstractStream<T> implements Stream<T> {
@@ -178,6 +179,47 @@ public BigDecimal aggregate(BigDecimal v, T t) {
         });
     }
 
+    @Override
+    public Byte average(final SelectorByte<T> selector) {
+        return (byte)(sum(selector) / count());
+    }
+
+    @Override
+    public Short average(SelectorShort<T> selector) {
+        return (short)(sum(selector) / count());
+    }
+
+    @Override
+    public Integer average(SelectorInteger<T> selector) {
+        return sum(selector) / count();
+    }
+
+    @Override
+    public Long average(SelectorLong<T> selector) {
+        return sum(selector) / count();
+    }
+
+    @Override
+    public Float average(SelectorFloat<T> selector) {
+        return sum(selector) / count();
+    }
+
+    @Override
+    public Double average(SelectorDouble<T> selector) {
+        return sum(selector) / count();
+    }
+
+    @Override
+    public BigDecimal average(SelectorBigDecimal<T> selector) {
+        //noinspection BigDecimalMethodWithoutRoundingCalled
+        return sum(selector).divide(new BigDecimal(count()));
+    }
+
+    @Override
+    public BigDecimal average(SelectorBigDecimal<T> selector, MathContext mathContext) {
+        return sum(selector).divide(new BigDecimal(count()), mathContext);
+    }
+
     @Override
     public <TResult extends Comparable<TResult>> T min(Selector<T, TResult> selector) {
         return orderBy(selector).first();

src/main/java/br/com/zbra/androidlinq/Stream.java

@@ -4,6 +4,7 @@
 import br.com.zbra.androidlinq.exception.MultipleElementsFoundException;
 
 import java.math.BigDecimal;
+import java.math.MathContext;
 import java.util.List;
 import java.util.Map;
 import java.util.NoSuchElementException;
@@ -203,6 +204,81 @@ interface Stream<T> extends Iterable<T> {
      */
     BigDecimal sum(SelectorBigDecimal<T> selector);
 
+    /**
+     * Computes the average of the sequence of Byte values that are obtained by invoking
+     * a transform function on each element of the input sequence.
+     *
+     * @param selector A transform function to apply to each element.
+     * @return The average of the projected values.
+     */
+    Byte average(SelectorByte<T> selector);
+
+    /**
+     * Computes the average of the sequence of Short values that are obtained by invoking
+     * a transform function on each element of the input sequence.
+     *
+     * @param selector A transform function to apply to each element.
+     * @return The average of the projected values.
+     */
+    Short average(SelectorShort<T> selector);
+
+    /**
+     * Computes the average of the sequence of Integer values that are obtained by invoking
+     * a transform function on each element of the input sequence.
+     *
+     * @param selector A transform function to apply to each element.
+     * @return The average of the projected values.
+     */
+    Integer average(SelectorInteger<T> selector);
+
+    /**
+     * Computes the average of the sequence of Long values that are obtained by invoking
+     * a transform function on each element of the input sequence.
+     *
+     * @param selector A transform function to apply to each element.
+     * @return The average of the projected values.
+     */
+    Long average(SelectorLong<T> selector);
+
+    /**
+     * Computes the average of the sequence of Float values that are obtained by invoking
+     * a transform function on each element of the input sequence.
+     *
+     * @param selector A transform function to apply to each element.
+     * @return The average of the projected values.
+     */
+    Float average(SelectorFloat<T> selector);
+
+    /**
+     * Computes the average of the sequence of Double values that are obtained by invoking
+     * a transform function on each element of the input sequence.
+     *
+     * @param selector A transform function to apply to each element.
+     * @return The average of the projected values.
+     */
+    Double average(SelectorDouble<T> selector);
+
+    /**
+     * Computes the average of the sequence of BigDecimal values that are obtained by invoking
+     * a transform function on each element of the input sequence.
+     *
+     * @param selector A transform function to apply to each element.
+     * @return The average of the projected values.
+     */
+    BigDecimal average(SelectorBigDecimal<T> selector);
+
+    /**
+     * Computes the average of the sequence of BigDecimal values that are obtained by invoking
+     * a transform function on each element of the input sequence.
+     *
+     * @param selector A transform function to apply to each element.
+     * @param mathContext Math context for operating with theses BigDecimals
+     * @return The average of the projected values.
+     * @see BigDecimal#divide(BigDecimal, MathContext)
+     * @see MathContext
+     */
+    BigDecimal average(SelectorBigDecimal<T> selector, MathContext mathContext);
+
     /**
      * Computes the min of the sequence of values that are obtained by invoking
      * a transform function on each element of the input sequence.

src/test/groovy/br/com/zbra/androidlinq/StreamTest.groovy

@@ -3,6 +3,9 @@ package br.com.zbra.androidlinq
 import br.com.zbra.androidlinq.delegate.*
 import br.com.zbra.androidlinq.exception.MultipleElementsFoundException
 
+import java.math.MathContext
+import java.math.RoundingMode
+
 import static br.com.zbra.androidlinq.Linq.stream as stream
 
 @SuppressWarnings("GroovyUnusedDeclaration")
@@ -300,6 +303,38 @@ class StreamTest extends GroovyTestCase {
         assert sum == stream(list).sum({ int n -> new BigDecimal(n) } as SelectorBigDecimal)
     }
 
+    void testAverage() {
+        def list = 0..9 as List<Integer>
+
+        // average Bytes
+        assert 4 == stream(list).average({ n -> (byte) n } as SelectorByte)
+
+        // average Shorts
+        assert 4 == stream(list).average({ n -> (short) n } as SelectorShort)
+
+        // average Integers
+        assert 4 == stream(list).average({ n -> (int) n } as SelectorInteger)
+
+        // average Longs
+        assert 4 == stream(list).average({ n -> (long) n } as SelectorLong)
+
+        // average Floats
+        assert 4.5 == stream(list).average({ n -> (float) n } as SelectorFloat)
+
+        // average Doubles
+        assert 4.5 == stream(list).average({ n -> (double) n } as SelectorDouble)
+
+        // average BigDecimals
+        assert new BigDecimal(4.5) == stream(list).average({ int n -> new BigDecimal(n) } as SelectorBigDecimal)
+
+        // average BigDecimals with MathContext
+        assert new BigDecimal(4.5) == stream(list).average({ int n -> new BigDecimal(n) } as SelectorBigDecimal, new MathContext(2, RoundingMode.HALF_UP))
+
+        // average BigDecimals with MathContext for recurring division
+        assert new BigDecimal(0.33, new MathContext(2, RoundingMode.UP)) == stream([0, 0, 1]).average({ int n -> new BigDecimal(n) } as SelectorBigDecimal, new MathContext(2, RoundingMode.UP))
+
+    }
+
     void testMax() {
 
         // max for numbers