scikit-learn
diff --git a/‎sklearn/tree/_criterion.pxd
+6-1 b/‎sklearn/tree/_criterion.pxd
+6-1
diff --git a/‎sklearn/tree/_criterion.pyx
+20-19 b/‎sklearn/tree/_criterion.pyx
+20-19
diff --git a/‎sklearn/tree/_splitter.pxd
+6-8 b/‎sklearn/tree/_splitter.pxd
+6-8
@@ -29,9 +29,13 @@ cdef class Criterion:
     cdef DOUBLE_t* sample_weight         # Sample weights
 
     cdef SIZE_t* samples                 # Sample indices in X, y
+    cdef SIZE_t* missing_samples         # Indices of missing-valued samples
     cdef SIZE_t start                    # samples[start:pos] are the samples in the left node
     cdef SIZE_t pos                      # samples[pos:end] are the samples in the right node
     cdef SIZE_t end
+    cdef SIZE_t missing_direction        # 0 Consider missing to be a part of left side of the split
+                                         # 1 Consider missing to be a part of right side of the split
+                                         # 2 Ingore missing value-ed samples.
 
     cdef SIZE_t n_outputs                # Number of outputs
     cdef SIZE_t n_node_samples           # Number of samples in the node (end-start)
@@ -57,7 +61,8 @@ cdef class Criterion:
                    SIZE_t end) nogil
     cdef void reset(self) nogil
     cdef void reverse_reset(self) nogil
-    cdef void update(self, SIZE_t new_pos) nogil
+    cdef void update_split_pos(self, SIZE_t new_pos) nogil
+    cdef void update_missing_direction(self, SIZE_t missing_direction) nogil
     cdef double node_impurity(self) nogil
     cdef void children_impurity(self, double* impurity_left,
                                 double* impurity_right) nogil
 
@@ -53,8 +53,8 @@ cdef class Criterion:
 
     cdef void init(self, DOUBLE_t* y, SIZE_t y_stride, DOUBLE_t* sample_weight,
                    double weighted_n_samples, SIZE_t* samples,
-                   SIZE_t start, SIZE_t end,
-                   SIZE_t start_missing, SIZE_t end_missing) nogil:
+                   SIZE_t* missing_samples, SIZE_t start, SIZE_t end,
+                   SIZE_t missing_direction) nogil:
         """Placeholder for a method which will initialize the criterion.
 
         Parameters
@@ -77,10 +77,12 @@ cdef class Criterion:
             The first non-missing-valued sample to be used on this node
         end: SIZE_t
             The last non-missing-valued sample used on this node
-        start_missing: SIZE_t
-            The first missing-valued sample to be used on this node
-        end_missing: SIZE_t
-            The last missing-valued sample used on this node
+        missing_direction: SIZE_t
+            The initial value of the direction in which the missing values 
+            must be sent to
+            0 - To send the missing values left
+            1 - To send the missing values right
+            2 - To ignore the missing values
 
         """
 
@@ -101,7 +103,7 @@ cdef class Criterion:
         """
         pass
 
-    cdef void update(self, SIZE_t new_pos) nogil:
+    cdef void update_split_pos(self, SIZE_t new_pos) nogil:
         """Updated statistics by moving samples[pos:new_pos] to the left child.
 
         This updates the collected statistics by moving samples[pos:new_pos]
@@ -116,18 +118,19 @@ cdef class Criterion:
 
         pass
 
-    cdef void move_missing(self, bint direction) nogil:
+    cdef void update_missing_direction(self, SIZE_t missing_direction) nogil:
         """Updated statistics by moving the missing-valued samples to l/r.
 
         This updates the collected statistics by moving the missing-valued
-        samples (samples[start_missing:end_nonmissing]) to the direction as
-        specified.
+        samples to the direction as specified.
 
         Parameters
         ----------
-        direction: bint
-            0 (false) to move the missing-valued samples left.
-            1 (true) to move the missing-valued samples right.
+        missing_direction: SIZE_t
+            Direction in which the missing values must be sent to
+            0 - To send the missing values left
+            1 - To send the missing values right
+            2 - To ignore the missing values
 
         """
 
@@ -254,12 +257,10 @@ cdef class ClassificationCriterion(Criterion):
         self.sample_weight = NULL
 
         self.samples = NULL
-        self.start_nonmissing = 0
-        self.pos_nonmissing = 0
-        self.end_nonmissing = 0
-
-        self.start_missing = 0
-        self.end_missing = 0
+        self.start = 0
+        self.pos = 0
+        self.end = 0
+        self.missing_direction = 2  # Ignore the missing values by default
 
         self.n_outputs = n_outputs
 
 
@@ -27,10 +27,11 @@ cdef struct SplitRecord:
                               # i.e. count of samples below threshold for feature.
                               # pos is >= end if the node is a leaf.
     double threshold          # Threshold to split at.
+    SIZE_t missing_direction  # Direction in which the missing values should
+                              # be sent to
     double improvement        # Impurity improvement given parent node.
     double impurity_left      # Impurity of the left split.
     double impurity_right     # Impurity of the right split.
-    double send_missing_left  # Whether to send the missing values left/right
 
 cdef class Splitter:
     # The splitter searches in the input space for a feature and a threshold
@@ -48,11 +49,10 @@ cdef class Splitter:
     cdef UINT32_t rand_r_state           # sklearn_rand_r random number state
 
     cdef SIZE_t* samples                 # Sample indices in X, y
+    cdef bint allow_missing              # Whether to include the missing vals
     cdef SIZE_t* missing_samples         # Sample indices with missing values
 
     cdef SIZE_t n_samples                # X.shape[0]
-    # TODO selfnote we need n_missing?
-
     cdef double weighted_n_samples       # Weighted number of samples
 
     cdef SIZE_t* features                # Feature indices in X
@@ -65,11 +65,8 @@ cdef class Splitter:
                                          # for the non missing values
     cdef SIZE_t end                      # End pos for the current node
                                          # for the non missing values
-
-    cdef SIZE_t start_missing            # Start position for the current node
-                                         # for the missing values
-    cdef SIZE_t end_missing              # End pos for the current node
-                                         # for the missing values
+    cdef SIZE_t missing_direction        # Direction in which the missing
+                                         # values must be sent to
 
     cdef bint presort                    # Whether to use presorting, only
                                          # allowed on dense data
@@ -104,6 +101,7 @@ cdef class Splitter:
                    object missing_samples) except *
 
     cdef void node_reset(self, SIZE_t start, SIZE_t end,
+                         SIZE_t missing_direction,
                          double* weighted_n_node_samples) nogil
 
     cdef void node_split(self,