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Preserve ordering function when converting to a TreeMap #110

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Merged
mperry merged 2 commits into from
Mar 22, 2015
Merged

Preserve ordering function when converting to a TreeMap #110

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5b7c6bc
Preserve ordering in TreeMap.toMutableMap()
dobesv Feb 20, 2015
7dd5bd8
Add a test case to verify that toMutableMap() works with keys that do…
dobesv Feb 20, 2015
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11 changes: 11 additions & 0 deletions core/src/main/java/fj/Ord.java
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Original file line number Diff line number Diff line change
Expand Up @@ -12,6 +12,7 @@

import java.math.BigDecimal;
import java.math.BigInteger;
import java.util.Comparator;

import static fj.Function.curry;

Expand Down Expand Up @@ -503,4 +504,14 @@ public static <A> Ord<A> hashEqualsOrd() {
});
}

class OrdComparator implements Comparator<A> {
@Override
public int compare(A o1, A o2) {
return Ord.this.compare(o1, o2).toInt();
}
}

public Comparator<A> toComparator() {
return new OrdComparator();
}
}
5 changes: 4 additions & 1 deletion core/src/main/java/fj/data/TreeMap.java
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Original file line number Diff line number Diff line change
Expand Up @@ -2,6 +2,7 @@

import fj.*;

import java.util.Comparator;
import java.util.Iterator;
import java.util.Map;

Expand Down Expand Up @@ -172,7 +173,9 @@ public Iterator<P2<K, V>> iterator() {
* @return A new mutable map isomorphic to this tree map.
*/
public Map<K, V> toMutableMap() {
final Map<K, V> m = new java.util.TreeMap<K, V>();
final F<K, P2<K, Option<V>>> fakePair = k -> P.p(k, Option.none());
final Comparator<K> comparator = tree.ord().comap(fakePair).toComparator();
final Map<K, V> m = new java.util.TreeMap<K, V>(comparator);
for (final P2<K, V> e : this) {
m.put(e._1(), e._2());
}
Expand Down
12 changes: 12 additions & 0 deletions core/src/test/java/fj/data/TreeMapTest.java
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Original file line number Diff line number Diff line change
@@ -1,13 +1,17 @@
package fj.data;

import java.util.Map;

import fj.Equal;
import fj.Ord;
import fj.P3;
import fj.Show;
import fj.P;

import org.junit.Test;

import static fj.data.Option.some;
import static org.junit.Assert.assertEquals;
import static org.junit.Assert.assertTrue;

/**
Expand Down Expand Up @@ -74,4 +78,12 @@ public void splitLookup() {
assertTrue(eq.eq(p3, P.p(leftMap, some(Integer.toString(pivot)), rightMap)));
}

@Test
public void toMutableMap() {
int max = 5;
List<List<Integer>> l = List.range(1, max + 1).map(n -> List.single(n));
TreeMap<List<Integer>, String> m2 = TreeMap.treeMap(Ord.listOrd(Ord.intOrd), l.zip(l.map(i -> i.toString())));
Map<List<Integer>, String> mm = m2.toMutableMap();
assertEquals(m2.keys().reverse(), List.iterableList(mm.keySet()));
}
}