Added rntuple_selector.js

demo/node/rntuple_selector.js

@@ -0,0 +1,93 @@
+import { readHeaderFooter, RBufferReader } from '../../modules/rntuple.mjs';
+import { R__unzip } from '../../modules/io.mjs';
+import { openFile } from 'jsroot';
+
+// Read and process the next data cluster from the RNTuple
+function readNextCluster(rntuple, selector) {
+  const builder = rntuple.builder,
+      clusterSummary = builder.clusterSummaries[selector.currentCluster],
+      pages = builder.pageLocations[selector.currentCluster][0].pages;
+
+  selector.currentCluster++;
+
+// Build flat array of [offset, size, offset, size, ...] to read pages
+  const dataToRead = pages.flatMap(p => [Number(p.locator.offset), Number(p.locator.size)]);
+
+return rntuple.$file.readBuffer(dataToRead).then(blobsRaw => {
+  const blobs = Array.isArray(blobsRaw) ? blobsRaw : [blobsRaw],
+        unzipPromises = blobs.map((blob, idx) => {
+          const numElements = Number(pages[idx].numElements);
+          return R__unzip(blob, 8 * numElements);
+        });
+
+  // Wait for all pages to be decompressed
+  return Promise.all(unzipPromises).then(unzipBlobs => {
+    const totalSize = unzipBlobs.reduce((sum, b) => sum + b.byteLength, 0),
+          flat = new Uint8Array(totalSize);
+
+    let offset = 0;
+    for (const blob of unzipBlobs) {
+      flat.set(new Uint8Array(blob.buffer || blob), offset);
+      offset += blob.byteLength;
+    }
+
+    // Create reader and deserialize doubles from the buffer
+    const reader = new RBufferReader(flat.buffer);
+    for (let i = 0; i < clusterSummary.numEntries; ++i) {
+      selector.tgtobj.myDouble = reader.readF64();
+      selector.Process();
+    }
+
+    selector.End();
+  });
+});
+}
+
+// TODO args can later be used to filter fields, limit entries, etc.
+// Create reader and deserialize doubles from the buffer
+function rntupleProcess(rntuple, selector, args) {
+  return readHeaderFooter(rntuple).then(() => {
+    selector.Begin();
+    selector.currentCluster = 0;
+    return readNextCluster(rntuple, selector, args);
+  });
+}
+
+// test block (runs only in node)
+if (typeof window === 'undefined') {
+  // Defining the object selector
+  const selector = {
+    tgtobj: {},
+    currentCluster: 0,
+    count: 0,
+    sum: 0,
+
+    Begin() {
+      console.log('Begin processing');
+    },
+
+    Process() {
+      console.log('Entry : ', this.tgtobj);
+      this.sum += this.tgtobj.myDouble;
+      this.count++;
+    },
+
+    End() {
+      if (this.count === 0)
+        console.error('No entries processed');
+      else
+        console.log(`Mean = ${(this.sum / this.count).toFixed(4)} from ${this.count} entries`);
+    }
+  };
+
+  openFile('./simple.root')
+    .then(file => file.readObject('myNtuple'))
+    .then(rntuple => {
+      if (!rntuple) throw new Error('myNtuple not found');
+      return rntupleProcess(rntuple, selector);
+    })
+    .then(() => console.log('RNTuple::Process finished'))
+    .catch(err => console.error(err));
+}
+
+export { rntupleProcess };