From 77409892b010c65427d70c0e3e13b828f5d2761f Mon Sep 17 00:00:00 2001 From: Stephan Hageboeck Date: Fri, 15 May 2026 15:26:02 +0200 Subject: [PATCH] [RelNotes] Mention the Rosetta stone for RDF. (cherry picked from commit ce90f346b6aeb19aaf84816fc6ec0179b28d59a1) --- README/ReleaseNotes/v640/index.md | 1 + 1 file changed, 1 insertion(+) diff --git a/README/ReleaseNotes/v640/index.md b/README/ReleaseNotes/v640/index.md index 552d98858453b..2960da59f7747 100644 --- a/README/ReleaseNotes/v640/index.md +++ b/README/ReleaseNotes/v640/index.md @@ -336,6 +336,7 @@ Given the risk of silently incorrect physics results, and the absence of known w ## RDataFrame +- The RDataFrame documentation now contains a section to help translate `TTree::Draw` expressions to RDataFrame, the ["Rosetta stone"](https://root.cern/doc/master/classROOT_1_1RDataFrame.html#rosetta-stone). - The change of default compression settings used by Snapshot for the TTree output data format introduced in 6.38 (was 101 before 6.38, became 505 in 6.38) is reverted. That choice was based on evidence available up to that point that indicated that ZSTD was outperforming ZLIB in all cases for the available datasets. New evidence demonstrated that this is not always the case, and in particular for the notable case of TTree branches made of collections where many (up to all) of them are empty. The investigation is described at https://github.com/vepadulano/ttree-lossless-compression-studies. The new default compression settings for Snapshot are respectively `kUndefined` for the compression algorithm and `0` for the compression level. When Snapshot detects `kUndefined` used in the options, it changes the compression settings to the new defaults of 101 (for TTree) and 505 (for RNTuple). - Signatures of the HistoND and HistoNSparseD operations have been changed. Previously, the list of input column names was allowed to contain an extra column for events weights. This was done to align the logic with the THnBase::Fill method. But this signature was inconsistent with all other Histo* operations, which have a separate function argument that represents the column to get the weights from. Thus, HistoND and HistoNSparseD both now have a separate function argument for the weights. The previous signature is still supported, but deprecated: a warning will be raised if the user passes the column name of the weights as an extra element of the list of input column names. In a future version of ROOT this functionality will be removed. From now on, creating a (sparse) N-dim histogram with weights should be done by calling `HistoN[Sparse]D(histoModel, inputColumns, weightColumn)`. - The string expressions passed to `Vary` calls can now be shortened. If the string begins with '{' and ends with '}' (excluding whitespace, tab and newline characters), RDataFrame will automatically inject the return type in the generated lambda expression before declaring it to the interpreter. This for example allows writing an expression such as `{{px * 0.9, px * 1.1}, {py * 0.9, py * 1.1}}` instead of `ROOT::RVec>>{{px * 0.9, px * 1.1}, {py * 0.9, py * 1.1}}`