data: withStretchedList

2 files changed, 37 insertions, 0 deletions

diff --git a/src/data/composite/data/index.js b/src/data/composite/data/index.js
index c80bb350..46a3dc81 100644
--- a/src/data/composite/data/index.js
+++ b/src/data/composite/data/index.js
@@ -18,6 +18,7 @@ export {default as withUniqueItemsOnly} from './withUniqueItemsOnly.js';
 export {default as withFilteredList} from './withFilteredList.js';
 export {default as withMappedList} from './withMappedList.js';
 export {default as withSortedList} from './withSortedList.js';
+export {default as withStretchedList} from './withStretchedList.js';
 
 export {default as withPropertyFromList} from './withPropertyFromList.js';
 export {default as withPropertiesFromList} from './withPropertiesFromList.js';
diff --git a/src/data/composite/data/withStretchedList.js b/src/data/composite/data/withStretchedList.js
new file mode 100644
index 00000000..46733064
--- /dev/null
+++ b/src/data/composite/data/withStretchedList.js
@@ -0,0 +1,36 @@
+// Repeats each item in a list in-place by a corresponding length.
+
+import {input, templateCompositeFrom} from '#composite';
+import {repeat, stitchArrays} from '#sugar';
+import {isNumber, validateArrayItems} from '#validators';
+
+export default templateCompositeFrom({
+  annotation: `withStretchedList`,
+
+  inputs: {
+    list: input({type: 'array'}),
+
+    lengths: input({
+      validate: validateArrayItems(isNumber),
+    }),
+  },
+
+  outputs: ['#stretchedList'],
+
+  steps: () => [
+    {
+      dependencies: [input('list'), input('lengths')],
+      compute: (continuation, {
+        [input('list')]: list,
+        [input('lengths')]: lengths,
+      }) => continuation({
+        ['#stretchedList']:
+          stitchArrays({
+            item: list,
+            length: lengths,
+          }).map(({item, length}) => repeat(length, [item]))
+            .flat(),
+      }),
+    },
+  ],
+});