Skip to content

Added List.partition #161

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
mperry merged 1 commit into from
Jun 24, 2015
Merged

Added List.partition #161

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
16 changes: 16 additions & 0 deletions core/src/main/java/fj/data/List.java
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -854,6 +854,22 @@ public final List<List<A>> partition(final int n) {
return unfold(as -> as.isEmpty() ? Option.<P2<List<A>, List<A>>>none() : some(as.splitAt(n)), this);
}

/**
* Partitions the list into a tuple where the first element contains the
* items that satisfy the the predicate f and the second element contains the
* items that does not. The relative order of the elements in the returned tuple
* is the same as the original list.
*
* @param f Predicate function.
*/
public P2<List<A>, List<A>> partition(F<A, Boolean> f) {
P2<List<A>, List<A>> p2 = foldLeft(acc -> a ->
f.f(a) ? P.p(acc._1().cons(a), acc._2()) : P.p(acc._1(), acc._2().cons(a)),
P.p(nil(), nil())
);
return P.p(p2._1().reverse(), p2._2().reverse());
}

/**
* Returns the list of initial segments of this list, shortest first.
*
Expand Down
11 changes: 11 additions & 0 deletions core/src/test/java/fj/data/ListTest.java
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -1,5 +1,7 @@
package fj.data;

import fj.Equal;
import fj.P2;
import org.junit.Test;

import java.util.Arrays;
Expand Down Expand Up @@ -53,4 +55,13 @@ public void convertToString() {
expected.append(')');
assertEquals(expected.toString(), List.range(0, n).toString());
}

@Test
public void partition() {
P2<List<Integer>, List<Integer>> p = List.range(1, 5).partition(i -> i % 2 == 0);
Equal<List<Integer>> e = Equal.listEqual(Equal.intEqual);
assertTrue(e.eq(p._1(), List.list(2, 4)));
assertTrue(e.eq(p._2(), List.list(1, 3)));
}

}