1 files changed, 51 insertions, 0 deletions
diff --git a/src/data/composite/data/fillMissingListItems.js b/src/data/composite/data/fillMissingListItems.js
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+++ b/src/data/composite/data/fillMissingListItems.js
@@ -0,0 +1,51 @@
+// Replaces items of a list, which are null or undefined, with some fallback
+// value. By default, this replaces the passed dependency.
+//
+// See also:
+//  - excludeFromList
+//
+// More list utilities:
+//  - withFlattenedList
+//  - withPropertyFromList
+//  - withPropertiesFromList
+//  - withUnflattenedList
+//
+
+import {input, templateCompositeFrom} from '#composite';
+
+export default templateCompositeFrom({
+  annotation: `fillMissingListItems`,
+
+  inputs: {
+    list: input({type: 'array'}),
+    fill: input({acceptsNull: true}),
+  },
+
+  outputs: ({
+    [input.staticDependency('list')]: list,
+  }) => [list ?? '#list'],
+
+  steps: () => [
+    {
+      dependencies: [input('list'), input('fill')],
+      compute: (continuation, {
+        [input('list')]: list,
+        [input('fill')]: fill,
+      }) => continuation({
+        ['#filled']:
+          list.map(item => item ?? fill),
+      }),
+    },
+
+    {
+      dependencies: [input.staticDependency('list'), '#filled'],
+      compute: (continuation, {
+        [input.staticDependency('list')]: list,
+        ['#filled']: filled,
+      }) => continuation({
+        [list ?? '#list']:
+          filled,
+      }),
+    },
+  ],
+});