Python R Data Structure Mapping

Python-R Data Structure Mapping

Summary

Convert between R Spectra objects and Python mass spectrometry data structures (matchms.Spectrum, spectrum_utils.MsmsSpectrum) to enable seamless execution of Python MS algorithms within R workflows. This skill bridges language barriers by serializing R objects, executing Python routines, and deserializing results back into R-compatible formats.

When to use

When you have mass spectrometry data in R's Spectra format but need to leverage Python libraries (matchms, spectrum_utils) for specialized operations like spectral similarity scoring, filtering, or normalization that lack native R implementations or perform better in Python. Particularly relevant when building custom workflows that integrate both R and Python MS packages in a single analysis pipeline.

When NOT to use

• The desired operation is already available in R's Spectra package (e.g., compareSpectra for native similarity scoring) — use native R functions to avoid serialization overhead.
• Python dependencies (matchms ≥0.31, spectrum_utils ≥0.3.2, numpy ≥2.2.0) cannot be installed on the system or are incompatible with the R environment.
• Real-time or streaming analysis on very large spectra collections where serialization/deserialization latency is prohibitive.

Inputs

• R Spectra object (containing MS/MS spectra with m/z, intensity, precursor m/z, and metadata)
• Python matchms or spectrum_utils library reference (pre-configured via reticulate)
• Tolerance/parameter settings for the target Python algorithm

Outputs

• R Spectra object (result of Python computation, with all attributes preserved)
• Numeric matrix of pairwise similarity scores (if using compareSpectriPy)
• Filtered or normalized Spectra object (if using Python filtering/normalization routines)

How to apply

Define an R function that accepts a Spectra object as input. Use SpectriPy's cross-language interface (powered by reticulate) to serialize the Spectra object into a Python-compatible structure (matchms.Spectrum or spectrum_utils.MsmsSpectrum). Execute the target Python routine on the converted data. Deserialize the Python result back into an R Spectra object, ensuring all expected attributes (msLevel, precursorMz, mz, intensity, metadata fields) are preserved and valid. Validate the round-trip by confirming schema integrity and comparing downstream calculations performed in both languages on identical input data.

Related tools

• SpectriPy (Provides the R-to-Python wrapping interface and conversion functions (compareSpectriPy, Spectra-to-matchms serialization)) — https://github.com/RforMassSpectrometry/SpectriPy
• Spectra (Defines the R data structure (Spectra objects, backends) that serve as input/output containers for cross-language conversion) — https://github.com/RforMassSpectrometry/Spectra
• reticulate (Underlying R package that manages Python environment configuration, object serialization, and function calls between R and Python)
• matchms (Python MS package providing spectral similarity algorithms (CosineGreedy, etc.) and spectrum object format that SpectriPy wraps) — https://github.com/matchms
• spectrum_utils (Python MS utilities library offering spectrum preprocessing and MsmsSpectrum object format compatible with SpectriPy conversion) — https://github.com/bittremieux-lab/spectrum_utils

Examples

library(Spectra); library(SpectriPy); all <- c(caf, mhd); res <- compareSpectriPy(all, caf, param = CosineGreedy(tolerance = 0.05))

Evaluation signals

• Returned Spectra object is valid (schema conforms to Spectra class requirements; no null/NaN in critical fields like msLevel, precursorMz, mz, intensity).
• Round-trip integrity: attributes present in input Spectra match those in output Spectra after Python round-trip conversion.
• Computational equivalence: similarity scores or filtering results from compareSpectriPy with CosineGreedy(tolerance=X) match expected values from direct Python matchms calls on identical spectra.
• No data loss: mz and intensity vectors preserve numeric precision and order after serialization/deserialization cycles.
• Metadata preservation: custom spectra variables (id, name, etc.) survive the round-trip conversion.

Limitations

• Requires Python ≥3.12 and manual installation of matching versions of matchms (0.31), spectrum_utils (0.3.2), and numpy (2.2.0); version mismatches can cause silent data corruption or conversion failures.
• No changelog available in SpectriPy repository, limiting reproducibility and version tracking across updates.
• Serialization/deserialization overhead makes this approach slower than pure R operations; most beneficial for algorithms unavailable in R rather than those that exist natively in Spectra.
• Cross-language object conversion may introduce floating-point precision artifacts or reordering of peaks if not carefully implemented; validate numerical stability for downstream quantitative comparisons.

Evidence

• [readme] SpectriPy enables seamless integration: "By wrapping Python functionality into R functions, SpectriPy allows a seamless integration of Python libraries into R"
• [other] Conversion workflow steps: "1. Define an R function that takes a Spectra object as input. 2. Use SpectriPy's cross-language interface to serialize the Spectra object and pass it to a Python MS package routine. 3. Execute the"
• [readme] Supported Python object formats: "contains functions to convert between R's Spectra::Spectra objects and matchms.Spectrum and spectrum_utils.spectrum.MsmsSpectrum objects from the Python matchms"
• [readme] Python dependency requirements: "SpectriPy needs Python (version >= 3.12) to be installed on the system. All necessary Python libraries (listed below) are automatically installed by the"
• [readme] Example usage with CosineGreedy: "res <- compareSpectriPy(all, caf, param = CosineGreedy(tolerance = 0.05))"