diff options
Diffstat (limited to 'src/main/java/bjc/data')
| -rw-r--r-- | src/main/java/bjc/data/CollectionUtils.java | 54 | ||||
| -rw-r--r-- | src/main/java/bjc/data/Holder.java | 4 |
2 files changed, 57 insertions, 1 deletions
diff --git a/src/main/java/bjc/data/CollectionUtils.java b/src/main/java/bjc/data/CollectionUtils.java new file mode 100644 index 0000000..08ef711 --- /dev/null +++ b/src/main/java/bjc/data/CollectionUtils.java @@ -0,0 +1,54 @@ +/* + * esodata - data structures of varying utility + * Copyright 2022, Ben Culkin + * + * This program is free software: you can redistribute it and/or modify + * it under the terms of the GNU General Public License as published by + * the Free Software Foundation, either version 3 of the License, or + * (at your option) any later version. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + * + * You should have received a copy of the GNU General Public License + * along with this program. If not, see <https://www.gnu.org/licenses/>. + */ +package bjc.data; + +import java.util.*; +import java.util.function.Function; + +/** + * Various utilities for dealing w/ collections + * @author bjcul + * + */ +public class CollectionUtils { + /** + * Create a function that converts a collection into a map. + * + * @param <Val> The type of the values in the map + * @param <Idx> The type of the keys in the map + * @param <Ent> The type of the values in the collection + * + * @param keyFunc The function that determines keys + * @param valFunc The function that determines values + * + * @return A function which uses the provided function to create a map from a + * collection. + */ + public static <Val, Idx, Ent> Function<Collection<Ent>, Map<Idx, Val>> indexBy(Function<Ent, Idx> keyFunc, + Function<Ent, Val> valFunc) { + return (coll) -> { + Map<Idx, Val> mep = new HashMap<>(); + + for (Ent ent : coll) { + mep.put(keyFunc.apply(ent), valFunc.apply(ent)); + } + + return mep; + }; + } +} diff --git a/src/main/java/bjc/data/Holder.java b/src/main/java/bjc/data/Holder.java index 4a1de75..57a5d6c 100644 --- a/src/main/java/bjc/data/Holder.java +++ b/src/main/java/bjc/data/Holder.java @@ -26,6 +26,7 @@ import bjc.data.internals.WrappedLazy; import bjc.data.internals.WrappedOption; import bjc.funcdata.FunctionalList; import bjc.funcdata.theory.Functor; +import bjc.typeclasses.Container; /** * A holder of a single value. @@ -35,7 +36,8 @@ import bjc.funcdata.theory.Functor; * @param <ContainedType> * The type of value held. */ -public interface Holder<ContainedType> extends Functor<ContainedType> { +public interface Holder<ContainedType> extends Functor<ContainedType>, Container<ContainedType, Holder<ContainedType>> { + // note: to really work, this should also take the binding parameter /** * Bind a function across the value in this container. * |