docs(examples): array group

examples/build/config/transform/array/group/config.jsonnet

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+// This example groups an array of arrays into an array of objects
+// based on index and configured keys.
+local sub = import '../../../../../../build/config/substation.libsonnet';
+
+local files_key = 'meta files';
+
+{
+  concurrency: 1,
+  transforms: [
+    // This example sends data to stdout at each step to iteratively show
+    // how the data is transformed.
+    sub.tf.send.stdout(),
+    // Copy the object to metadata, where it is grouped.
+    sub.tf.obj.cp({ object: { target_key: files_key } }),
+    // Elements from the file_name array are transformed and derived file extensions
+    // are added to a new array.
+    sub.tf.meta.for_each({
+      object: { source_key: sub.helpers.object.get_element(files_key, 'file_name'), target_key: sub.helpers.object.append(files_key, 'file_extension') },
+      transform: sub.tf.string.capture(settings={ pattern: '\\.([^\\.]+)$' }),
+    }),
+    // The arrays grouped into an array of objects, then copied to the message's data field.
+    // For example:
+    //
+    // [{name: name1, type: type1, size: size1, extension: extension1}, {name: name2, type: type2, size: size2, extension: extension2}]
+    sub.tf.object.cp({ object: { source_key: files_key + '|@group' } }),
+    sub.tf.send.stdout(),
+  ],
+}

examples/build/config/transform/array/group/data.json

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+{"file_name":["foo.txt","bar.html"],"file_type":["text/plain","text/html"],"file_size":[100,500]}