# Source code for matchms.similarity.ParentMassMatch

```from typing import List
import numba
import numpy
from matchms.typing import SpectrumType
from .BaseSimilarity import BaseSimilarity

[docs]class ParentMassMatch(BaseSimilarity):
"""Return True if spectrums match in parent mass (within tolerance), and False otherwise.

Example to calculate scores between 2 spectrums and iterate over the scores

.. testcode::

import numpy as np
from matchms import calculate_scores
from matchms import Spectrum
from matchms.similarity import ParentMassMatch

spectrum_1 = Spectrum(mz=np.array([]),
intensities=np.array([]),
spectrum_2 = Spectrum(mz=np.array([]),
intensities=np.array([]),
spectrum_3 = Spectrum(mz=np.array([]),
intensities=np.array([]),
spectrum_4 = Spectrum(mz=np.array([]),
intensities=np.array([]),
references = [spectrum_1, spectrum_2]
queries = [spectrum_3, spectrum_4]

similarity_score = ParentMassMatch(tolerance=5.0)
scores = calculate_scores(references, queries, similarity_score)

for (reference, query, score) in scores:
print(f"Parentmass match between {reference.get('id')} and {query.get('id')}" +
f" is {score:.2f}")

Should output

.. testoutput::

Parentmass match between 1 and 3 is 1.00
Parentmass match between 1 and 4 is 0.00
Parentmass match between 2 and 3 is 0.00
Parentmass match between 2 and 4 is 1.00

"""
# Set key characteristics as class attributes
is_commutative = True
# Set output data type, e.g.  "float" or [("score", "float"), ("matches", "int")]
score_datatype = bool

[docs]    def __init__(self, tolerance: float = 0.1):
"""
Parameters
----------
tolerance
Specify tolerance below which two masses are counted as match.
"""
self.tolerance = tolerance

[docs]    def pair(self, reference: SpectrumType, query: SpectrumType) -> float:
"""Compare parent masses between reference and query spectrum.

Parameters
----------
reference
Single reference spectrum.
query
Single query spectrum.
"""
parentmass_ref = reference.get("parent_mass")
parentmass_query = query.get("parent_mass")
assert parentmass_ref is not None and parentmass_query is not None, "Missing parent mass."

score = abs(parentmass_ref - parentmass_query) <= self.tolerance
return numpy.asarray(score, dtype=self.score_datatype)

[docs]    def matrix(self, references: List[SpectrumType], queries: List[SpectrumType],
is_symmetric: bool = False) -> numpy.ndarray:
"""Compare parent masses between all references and queries.

Parameters
----------
references
List/array of reference spectrums.
queries
List/array of Single query spectrums.
is_symmetric
Set to True when *references* and *queries* are identical (as for instance for an all-vs-all
comparison). By using the fact that score[i,j] = score[j,i] the calculation will be about
2x faster.
"""
def collect_parentmasses(spectrums):
"""Collect parentmasses."""
parentmasses = []
for spectrum in spectrums:
parentmass = spectrum.get("parent_mass")
assert parentmass is not None, "Missing parent mass."
parentmasses.append(parentmass)
return numpy.asarray(parentmasses)

parentmasses_ref = collect_parentmasses(references)
parentmasses_query = collect_parentmasses(queries)
if is_symmetric:
return parentmass_scores_symmetric(parentmasses_ref, parentmasses_query,
self.tolerance).astype(self.score_datatype)
return parentmass_scores(parentmasses_ref, parentmasses_query,
self.tolerance).astype(self.score_datatype)

@numba.njit
def parentmass_scores(parentmasses_ref, parentmasses_query, tolerance):
scores = numpy.zeros((len(parentmasses_ref), len(parentmasses_query)))
for i, parentmass_ref in enumerate(parentmasses_ref):
for j, parentmass_query in enumerate(parentmasses_query):
scores[i, j] = (abs(parentmass_ref - parentmass_query) <= tolerance)
return scores

@numba.njit
def parentmass_scores_symmetric(parentmasses_ref, parentmasses_query, tolerance):
scores = numpy.zeros((len(parentmasses_ref), len(parentmasses_query)))
for i, parentmass_ref in enumerate(parentmasses_ref):
for j in range(i, len(parentmasses_query)):
scores[i, j] = (abs(parentmass_ref - parentmasses_query[j]) <= tolerance)
scores[j, i] = scores[i, j]
return scores
```