[MRG+1] EHN add decimals parameter for export_graphviz (scikit-learn#8698)

* EHN add decimals parameter for export_graphviz

* FIX address comments

* TST add test for classification

* TST/FIX address comments

* FIX comments raghav

Author: glemaitre

sklearn/tree/export.py

@@ -11,6 +11,8 @@
 #          Li Li <aiki.nogard@gmail.com>
 # License: BSD 3 clause
 
+from numbers import Integral
+
 import numpy as np
 import warnings
 
@@ -73,7 +75,7 @@ def export_graphviz(decision_tree, out_file=SENTINEL, max_depth=None,
                     feature_names=None, class_names=None, label='all',
                     filled=False, leaves_parallel=False, impurity=True,
                     node_ids=False, proportion=False, rotate=False,
-                    rounded=False, special_characters=False):
+                    rounded=False, special_characters=False, precision=3):
     """Export a decision tree in DOT format.
 
     This function generates a GraphViz representation of the decision tree,
@@ -143,6 +145,10 @@ def export_graphviz(decision_tree, out_file=SENTINEL, max_depth=None,
         When set to ``False``, ignore special characters for PostScript
         compatibility.
 
+    precision : int, optional (default=3)
+        Number of digits of precision for floating point in the values of
+        impurity, threshold and value attributes of each node.
+
     Returns
     -------
     dot_data : string
@@ -162,6 +168,7 @@ def export_graphviz(decision_tree, out_file=SENTINEL, max_depth=None,
     >>> clf = clf.fit(iris.data, iris.target)
     >>> tree.export_graphviz(clf,
     ...     out_file='tree.dot')                # doctest: +SKIP
+
     """
 
     def get_color(value):
@@ -226,7 +233,8 @@ def node_to_str(tree, node_id, criterion):
                                        characters[2])
             node_string += '%s %s %s%s' % (feature,
                                            characters[3],
-                                           round(tree.threshold[node_id], 4),
+                                           round(tree.threshold[node_id],
+                                                 precision),
                                            characters[4])
 
         # Write impurity
@@ -237,7 +245,7 @@ def node_to_str(tree, node_id, criterion):
                 criterion = "impurity"
             if labels:
                 node_string += '%s = ' % criterion
-            node_string += (str(round(tree.impurity[node_id], 4)) +
+            node_string += (str(round(tree.impurity[node_id], precision)) +
                             characters[4])
 
         # Write node sample count
@@ -260,16 +268,16 @@ def node_to_str(tree, node_id, criterion):
             node_string += 'value = '
         if tree.n_classes[0] == 1:
             # Regression
-            value_text = np.around(value, 4)
+            value_text = np.around(value, precision)
         elif proportion:
             # Classification
-            value_text = np.around(value, 2)
+            value_text = np.around(value, precision)
         elif np.all(np.equal(np.mod(value, 1), 0)):
             # Classification without floating-point weights
             value_text = value.astype(int)
         else:
             # Classification with floating-point weights
-            value_text = np.around(value, 4)
+            value_text = np.around(value, precision)
         # Strip whitespace
         value_text = str(value_text.astype('S32')).replace("b'", "'")
         value_text = value_text.replace("' '", ", ").replace("'", "")
@@ -402,6 +410,14 @@ def recurse(tree, node_id, criterion, parent=None, depth=0):
             return_string = True
             out_file = six.StringIO()
 
+        if isinstance(precision, Integral):
+            if precision < 0:
+                raise ValueError("'precision' should be greater or equal to 0."
+                                 " Got {} instead.".format(precision))
+        else:
+            raise ValueError("'precision' should be an integer. Got {}"
+                             " instead.".format(type(precision)))
+
         # Check length of feature_names before getting into the tree node
         # Raise error if length of feature_names does not match
         # n_features_ in the decision_tree

sklearn/tree/tests/test_export.py

@@ -2,14 +2,18 @@
 Testing for export functions of decision trees (sklearn.tree.export).
 """
 
-from re import finditer
+from re import finditer, search
 
+from numpy.random import RandomState
+
+from sklearn.base import ClassifierMixin
 from sklearn.tree import DecisionTreeClassifier, DecisionTreeRegressor
 from sklearn.ensemble import GradientBoostingClassifier
 from sklearn.tree import export_graphviz
 from sklearn.externals.six import StringIO
-from sklearn.utils.testing import assert_in, assert_equal, assert_raises
-from sklearn.utils.testing import assert_raise_message
+from sklearn.utils.testing import (assert_in, assert_equal, assert_raises,
+                                   assert_less_equal, assert_raises_regex,
+                                   assert_raise_message)
 from sklearn.exceptions import NotFittedError
 
 # toy sample
@@ -235,6 +239,13 @@ def test_graphviz_errors():
     out = StringIO()
     assert_raises(IndexError, export_graphviz, clf, out, class_names=[])
 
+    # Check precision error
+    out = StringIO()
+    assert_raises_regex(ValueError, "should be greater or equal",
+                        export_graphviz, clf, out, precision=-1)
+    assert_raises_regex(ValueError, "should be an integer",
+                        export_graphviz, clf, out, precision="1")
+
 
 def test_friedman_mse_in_graphviz():
     clf = DecisionTreeRegressor(criterion="friedman_mse", random_state=0)
@@ -249,3 +260,48 @@ def test_friedman_mse_in_graphviz():
 
     for finding in finditer("\[.*?samples.*?\]", dot_data.getvalue()):
         assert_in("friedman_mse", finding.group())
+
+
+def test_precision():
+
+    rng_reg = RandomState(2)
+    rng_clf = RandomState(8)
+    for X, y, clf in zip(
+            (rng_reg.random_sample((5, 2)),
+             rng_clf.random_sample((1000, 4))),
+            (rng_reg.random_sample((5, )),
+             rng_clf.randint(2, size=(1000, ))),
+            (DecisionTreeRegressor(criterion="friedman_mse", random_state=0,
+                                   max_depth=1),
+             DecisionTreeClassifier(max_depth=1, random_state=0))):
+
+        clf.fit(X, y)
+        for precision in (4, 3):
+            dot_data = export_graphviz(clf, out_file=None, precision=precision,
+                                       proportion=True)
+
+            # With the current random state, the impurity and the threshold
+            # will have the number of precision set in the export_graphviz
+            # function. We will check the number of precision with a strict
+            # equality. The value reported will have only 2 precision and
+            # therefore, only a less equal comparison will be done.
+
+            # check value
+            for finding in finditer("value = \d+\.\d+", dot_data):
+                assert_less_equal(
+                    len(search("\.\d+", finding.group()).group()),
+                    precision + 1)
+            # check impurity
+            if isinstance(clf, ClassifierMixin):
+                pattern = "gini = \d+\.\d+"
+            else:
+                pattern = "friedman_mse = \d+\.\d+"
+
+            # check impurity
+            for finding in finditer(pattern, dot_data):
+                assert_equal(len(search("\.\d+", finding.group()).group()),
+                             precision + 1)
+            # check threshold
+            for finding in finditer("<= \d+\.\d+", dot_data):
+                assert_equal(len(search("\.\d+", finding.group()).group()),
+                             precision + 1)