data, test: withUniqueItemsOnly (#composite/data)

2 files changed, 41 insertions, 0 deletions

diff --git a/src/data/composite/data/index.js b/src/data/composite/data/index.js
index db1c37cc..e2927afd 100644
--- a/src/data/composite/data/index.js
+++ b/src/data/composite/data/index.js
@@ -11,3 +11,4 @@ export {default as withPropertiesFromObject} from './withPropertiesFromObject.js
 export {default as withPropertyFromList} from './withPropertyFromList.js';
 export {default as withPropertyFromObject} from './withPropertyFromObject.js';
 export {default as withUnflattenedList} from './withUnflattenedList.js';
+export {default as withUniqueItemsOnly} from './withUniqueItemsOnly.js';
diff --git a/src/data/composite/data/withUniqueItemsOnly.js b/src/data/composite/data/withUniqueItemsOnly.js
new file mode 100644
index 00000000..7ee08b08
--- /dev/null
+++ b/src/data/composite/data/withUniqueItemsOnly.js
@@ -0,0 +1,40 @@
+// Excludes duplicate items from a list and provides the results, overwriting
+// the list in-place, if possible.
+
+import {input, templateCompositeFrom} from '#composite';
+import {unique} from '#sugar';
+
+export default templateCompositeFrom({
+  annotation: `withUniqueItemsOnly`,
+
+  inputs: {
+    list: input({type: 'array'}),
+  },
+
+  outputs: ({
+    [input.staticDependency('list')]: list,
+  }) => [list ?? '#uniqueItems'],
+
+  steps: () => [
+    {
+      dependencies: [input('list')],
+      compute: (continuation, {
+        [input('list')]: list,
+      }) => continuation({
+        ['#values']:
+          unique(list),
+      }),
+    },
+
+    {
+      dependencies: ['#values', input.staticDependency('list')],
+      compute: (continuation, {
+        '#values': values,
+        [input.staticDependency('list')]: list,
+      }) => continuation({
+        [list ?? '#uniqueItems']:
+          values,
+      }),
+    },
+  ],
+});