PersistenceLengths and its unitary tests

src/python/gudhi/representations/vector_methods.py

@@ -73,7 +73,7 @@ def transform(self, X):
 
         Parameters:
             X (list of n x 2 numpy arrays): input persistence diagrams.
-    
+
         Returns:
             numpy array with shape (number of diagrams) x (number of pixels = **resolution[0]** x **resolution[1]**): output persistence images.
         """
@@ -196,7 +196,7 @@ def transform(self, X):
 
         Parameters:
             X (list of n x 2 numpy arrays): input persistence diagrams.
-    
+
         Returns:
             numpy array with shape (number of diagrams) x (number of samples = **num_landscapes** x **resolution**): output persistence landscapes.
         """
@@ -271,7 +271,7 @@ def transform(self, X):
 
         Parameters:
             X (list of n x 2 numpy arrays): input persistence diagrams.
-    
+
         Returns:
             numpy array with shape (number of diagrams) x (**resolution**): output persistence silhouettes.
         """
@@ -363,7 +363,7 @@ def fit(self, X, y = None):
 
         if self.predefined_grid is None:
             if self.resolution is None: # Flexible/exact version
-                self.grid_ = np.unique(np.concatenate([pd.ravel() for pd in X] + [[-np.inf]], axis=0)) 
+                self.grid_ = np.unique(np.concatenate([pd.ravel() for pd in X] + [[-np.inf]], axis=0))
             else:
                 _grid_from_sample_range(self, X)
         else:
@@ -391,7 +391,7 @@ def transform(self, X):
 
             print("Empty list: output has shape [0, len(grid)]")
             return np.zeros((N, len(self.grid_)))
-            
+
         else:
 
             events = np.concatenate([pd.ravel(order="F") for pd in X], axis=0)
@@ -413,7 +413,7 @@ def transform(self, X):
                     i += 1
                 for k in range(0, N):
                     bettis[k].append(bettis[k][-1])
-    
+
             return np.array(bettis, dtype=int)[:, 0:-1]
 
     def fit_transform(self, X, y = None):
@@ -485,7 +485,7 @@ def __init__(self, mode="scalar", normalized=True, resolution=100, sample_range=
 
         Parameters:
             mode (string): what entropy to compute: either "scalar" for computing the entropy statistics, or "vector" for computing the entropy summary functions (default "scalar").
-            normalized (bool): whether to normalize the entropy summary function (default True). Used only if **mode** = "vector". 
+            normalized (bool): whether to normalize the entropy summary function (default True). Used only if **mode** = "vector".
             resolution (int): number of sample for the entropy summary function (default 100). Used only if **mode** = "vector".
             sample_range ([double, double]): minimum and maximum of the entropy summary function domain, of the form [x_min, x_max] (default [numpy.nan, numpy.nan]). It is the interval on which samples will be drawn evenly. If one of the values is numpy.nan, it can be computed from the persistence diagrams with the fit() method. Used only if **mode** = "vector".
             keep_endpoints (bool): when computing `sample_range`, use the exact extremities. This is mostly useful for plotting, the default is to use a slightly smaller range.
@@ -515,16 +515,16 @@ def transform(self, X):
 
         Parameters:
             X (list of n x 2 numpy arrays): input persistence diagrams.
-    
+
         Returns:
             numpy array with shape (number of diagrams) x (1 if **mode** = "scalar" else **resolution**): output entropy.
         """
         num_diag, Xfit = len(X), []
-        new_X = BirthPersistenceTransform().fit_transform(X)        
+        new_X = BirthPersistenceTransform().fit_transform(X)
 
         for i in range(num_diag):
             orig_diagram, new_diagram, num_pts_in_diag = X[i], new_X[i], X[i].shape[0]
-                
+
             p = new_diagram[:,1]
             p = p/np.sum(p)
             if self.mode == "scalar":
@@ -566,7 +566,7 @@ def __init__(self, threshold=10):
         Constructor for the TopologicalVector class.
 
         Parameters:
-            threshold (int): number of distances to keep (default 10). This is the dimension of the topological vector. If -1, this threshold is computed from the list of persistence diagrams by considering the one with the largest number of points and using the dimension of its corresponding topological vector as threshold. 
+            threshold (int): number of distances to keep (default 10). This is the dimension of the topological vector. If -1, this threshold is computed from the list of persistence diagrams by considering the one with the largest number of points and using the dimension of its corresponding topological vector as threshold.
         """
         self.threshold = threshold
 
@@ -586,7 +586,7 @@ def transform(self, X):
 
         Parameters:
             X (list of n x 2 numpy arrays): input persistence diagrams.
-    
+
         Returns:
             numpy array with shape (number of diagrams) x (**threshold**): output topological vectors.
         """
@@ -638,7 +638,7 @@ def __init__(self, polynomial_type="R", threshold=10):
 
         Parameters:
            polynomial_type (char): either "R", "S" or "T" (default "R"). Type of complex polynomial that is going to be computed (explained in https://link.springer.com/chapter/10.1007%2F978-3-319-23231-7_27).
-           threshold (int): number of coefficients (default 10). This is the dimension of the complex vector of coefficients, i.e. the number of coefficients corresponding to the largest degree terms of the polynomial. If -1, this threshold is computed from the list of persistence diagrams by considering the one with the largest number of points and using the dimension of its corresponding complex vector of coefficients as threshold. 
+           threshold (int): number of coefficients (default 10). This is the dimension of the complex vector of coefficients, i.e. the number of coefficients corresponding to the largest degree terms of the polynomial. If -1, this threshold is computed from the list of persistence diagrams by considering the one with the largest number of points and using the dimension of its corresponding complex vector of coefficients as threshold.
         """
         self.threshold, self.polynomial_type = threshold, polynomial_type
 
@@ -658,7 +658,7 @@ def transform(self, X):
 
         Parameters:
             X (list of n x 2 numpy arrays): input persistence diagrams.
-    
+
         Returns:
             numpy array with shape (number of diagrams) x (**threshold**): output complex vectors of coefficients.
         """
@@ -681,9 +681,9 @@ def transform(self, X):
                 roots = np.multiply(  (D[:,1]-D[:,0])/2, np.cos(alpha) - np.sin(alpha) + 1j * (np.cos(alpha) + np.sin(alpha))  )
             coeff = [0] * (N+1)
             coeff[N] = 1
-            for i in range(1, N+1): 
-                for j in range(N-i-1, N): 
-                    coeff[j] += ((-1) * roots[i-1] * coeff[j+1])   
+            for i in range(1, N+1):
+                for j in range(N-i-1, N):
+                    coeff[j] += ((-1) * roots[i-1] * coeff[j+1])
             coeff = np.array(coeff[::-1])[1:]
             Xfit[d, :min(thresh, coeff.shape[0])] = coeff[:min(thresh, coeff.shape[0])]
         return Xfit
@@ -885,3 +885,69 @@ def transform(self, X, sample_weight=None):
 
     def get_feature_names_out(self):
         return self._running_transform_names
+
+class PersistenceLengths(BaseEstimator, TransformerMixin):
+    """
+    This is a class that returns the sorted N-longest persistence lengths. If the input does not contain enough values,
+    the output will be filled with zeros.
+    """
+
+    def __init__(self, num_lengths=5):
+        """
+        Constructor for the PersistenceLengths class.
+
+        Parameters:
+            num_lengths (int): number of persistence lengths to return (default 5).
+
+        :raises ValueError: If num_lengths is lower or equal to 0.
+        """
+        if num_lengths <= 0:
+            raise ValueError("num_lengths must be greater than 0.")
+        self.num_lengths = num_lengths
+
+    def fit(self, X, y=None):
+        """
+        Fit the PersistenceLengths class on a list of persistence diagrams (this function actually does nothing but is
+        useful when PersistenceLengths is included in a scikit-learn Pipeline).
+
+        Parameters:
+            X (list of n x 2 numpy arrays): input persistence diagrams.
+            y (None): Ignored.
+        """
+        return self
+
+    def transform(self, X):
+        """
+        Compute the persistence lengths for each persistence diagram individually.
+
+        Parameters:
+            X (list of n x 2 numpy arrays): input persistence diagrams.
+
+        Returns:
+            numpy array with shape (number of diagrams) x (num_lengths): output persistence lengths.
+        """
+        pers_length_array = np.zeros((len(X), self.num_lengths))
+        for idx, pd in enumerate(X):
+            pl = pd[:, 1] - pd[:, 0]
+            if len(pl) >= self.num_lengths:
+                # Select the num_lengths biggest persistence bars length
+                pl = np.partition(pl, -self.num_lengths)[-self.num_lengths :]
+
+            # Sort in reverse order persistence lengths (where length = death - birth)
+            pl = np.flip(np.sort(pl))
+            # Filled with zeros if not enough values
+            pers_length_array[idx][:len(pl)] = pl
+
+        return pers_length_array
+
+    def __call__(self, diag):
+        """
+        Apply PersistenceLengths on a single persistence diagram and outputs the result.
+
+        Parameters:
+            diag (n x 2 numpy array): input persistence diagram.
+
+        Returns:
+            numpy 1d array of length num_lengths: output persistence lengths.
+        """
+        return self.transform([diag])[0]

src/python/test/test_representations.py

@@ -9,7 +9,7 @@
 
 # Vectorization
 from gudhi.representations import (Landscape, Silhouette, BettiCurve, ComplexPolynomial,\
-  TopologicalVector, PersistenceImage, Entropy)
+  TopologicalVector, PersistenceImage, Entropy, PersistenceLengths)
 
 # Preprocessing
 from gudhi.representations import (BirthPersistenceTransform, Clamping, DiagramScaler, Padding, ProminentPoints, \
@@ -128,8 +128,8 @@ def test_atol_doc():
 
     # Check the center of the first_cluster and second_cluster are in Atol centers
     centers = atol_vectoriser.fit(X=[a, b, c]).centers
-    np.isclose(centers, first_cluster.mean(axis=0)).all(1).any() 
-    np.isclose(centers, second_cluster.mean(axis=0)).all(1).any() 
+    np.isclose(centers, first_cluster.mean(axis=0)).all(1).any()
+    np.isclose(centers, second_cluster.mean(axis=0)).all(1).any()
 
     vectorization = atol_vectoriser.transform(X=[a, b, c])
     assert np.allclose(vectorization[0], atol_vectoriser(a))
@@ -203,7 +203,7 @@ def test_vectorization_empty_diagrams():
     scv = Entropy(mode="vector", normalized=False, resolution=random_resolution)(empty_diag)
     assert not np.any(scv)
     assert scv.shape[0] == random_resolution
-    
+
 def test_entropy_miscalculation():
     diag_ex = np.array([[0.0,1.0], [0.0,1.0], [0.0,2.0]])
     def pe(pd):
@@ -215,14 +215,14 @@ def pe(pd):
     sce = Entropy(mode="vector", resolution=4, normalized=False, keep_endpoints=True)
     pef = [-1/4*np.log(1/4)-1/4*np.log(1/4)-1/2*np.log(1/2),
            -1/4*np.log(1/4)-1/4*np.log(1/4)-1/2*np.log(1/2),
-           -1/2*np.log(1/2), 
+           -1/2*np.log(1/2),
            0.0]
     assert all(([pef] == sce.fit_transform([diag_ex]))[0])
     sce = Entropy(mode="vector", resolution=4, normalized=True)
     pefN = (sce.fit_transform([diag_ex]))[0]
     area = np.linalg.norm(pefN, ord=1)
     assert area==pytest.approx(1)
-        
+
 def test_kernel_empty_diagrams():
     empty_diag = np.empty(shape = [0, 2])
     assert SlicedWassersteinDistance(num_directions=100)(empty_diag, empty_diag) == 0.
@@ -318,3 +318,18 @@ def test_endpoints():
 def test_get_params():
     for vec in [ Landscape(), Silhouette(), BettiCurve(), Entropy(mode="vector") ]:
         vec.get_params()
+
+def test_persistence_lengths():
+    diag = np.array([[3., 5.], [0, np.inf], [4., 4.], [2., 6.]])
+    for nl in range(1, 6):
+        pl = PersistenceLengths(num_lengths=nl)(diag)
+        # test the result is sorted
+        assert np.all(sorted(pl, reverse=True) == pl)
+        if len(pl) > 0:
+            assert np.isinf(pl[0])
+        for idx in range(len(pl)):
+            if idx >= len(diag):
+                # test it is filled with zeros when going further the input
+                assert pl[idx] == 0.
+    with pytest.raises(ValueError):
+        pl = PersistenceLengths(num_lengths=0)(diag)