Add petab.Problem.n_{estimated,measurements,priors} (#243)

Makes it more convenient to compute model selection criteria.

Author: dweindl

petab/problem.py

@@ -1004,3 +1004,21 @@ def scale_parameters(
             )
             for parameter_id, parameter_value in x_dict.items()
         }
+
+    @property
+    def n_estimated(self) -> int:
+        """The number of estimated parameters."""
+        return len(self.x_free_indices)
+
+    @property
+    def n_measurements(self) -> int:
+        """Number of measurements."""
+        return self.measurement_df[MEASUREMENT].notna().sum()
+
+    @property
+    def n_priors(self) -> int:
+        """Number of priors."""
+        if OBJECTIVE_PRIOR_PARAMETERS not in self.parameter_df:
+            return 0
+
+        return self.parameter_df[OBJECTIVE_PRIOR_PARAMETERS].notna().sum()

tests/test_petab.py

@@ -46,6 +46,7 @@ def petab_problem():
     measurement_df = pd.DataFrame(
         data={
             OBSERVABLE_ID: ["obs1", "obs2"],
+            MEASUREMENT: [0.1, 0.2],
             OBSERVABLE_PARAMETERS: ["", "p1;p2"],
             NOISE_PARAMETERS: ["p3;p4", "p5"],
         }
@@ -63,6 +64,7 @@ def petab_problem():
         data={
             PARAMETER_ID: ["dynamicParameter1", "dynamicParameter2"],
             PARAMETER_NAME: ["", "..."],
+            ESTIMATE: [1, 0],
         }
     ).set_index(PARAMETER_ID)
 
@@ -92,13 +94,18 @@ def petab_problem():
         petab.write_observable_df(observable_df, observable_file_name)
 
         with pytest.deprecated_call():
-            yield petab.Problem.from_files(
+            petab_problem = petab.Problem.from_files(
                 sbml_file=sbml_file_name,
                 measurement_file=measurement_file_name,
                 condition_file=condition_file_name,
                 parameter_file=parameter_file_name,
                 observable_files=observable_file_name,
             )
+            assert petab_problem.n_measurements == 2
+            assert petab_problem.n_estimated == 1
+            assert petab_problem.n_priors == 0
+
+            yield petab_problem
 
 
 @pytest.fixture