Fix dask prediction. (#4941)

* Fix dask prediction.

* Add better error messages for wrong partition.

demo/dask/cpu_training.py

@@ -7,11 +7,10 @@ from dask import array as da
 
 def main(client):
     # generate some random data for demonstration
-    n = 100
     m = 100000
-    partition_size = 1000
-    X = da.random.random((m, n), partition_size)
-    y = da.random.random(m, partition_size)
+    n = 100
+    X = da.random.random(size=(m, n), chunks=100)
+    y = da.random.random(size=(m, ), chunks=100)
 
     # DaskDMatrix acts like normal DMatrix, works as a proxy for local
     # DMatrix scatter around workers.
@@ -38,6 +37,6 @@ def main(client):
 
 if __name__ == '__main__':
     # or use other clusters for scaling
-    with LocalCluster(n_workers=4, threads_per_worker=1) as cluster:
+    with LocalCluster(n_workers=7, threads_per_worker=1) as cluster:
         with Client(cluster) as client:
             main(client)

demo/dask/gpu_training.py

@@ -6,11 +6,11 @@ from xgboost.dask import DaskDMatrix
 
 
 def main(client):
-    n = 100
+    # generate some random data for demonstration
     m = 100000
-    partition_size = 1000
-    X = da.random.random((m, n), partition_size)
-    y = da.random.random(m, partition_size)
+    n = 100
+    X = da.random.random(size=(m, n), chunks=100)
+    y = da.random.random(size=(m, ), chunks=100)
 
     # DaskDMatrix acts like normal DMatrix, works as a proxy for local
     # DMatrix scatter around workers.
@@ -23,6 +23,7 @@ def main(client):
     output = xgb.dask.train(client,
                             {'verbosity': 2,
                              'nthread': 1,
+                             # Golden line for GPU training
                              'tree_method': 'gpu_hist'},
                             dtrain,
                             num_boost_round=4, evals=[(dtrain, 'train')])

python-package/xgboost/dask.py

@@ -139,13 +139,14 @@ class DaskDMatrix:
         self._missing = missing
 
         if len(data.shape) != 2:
-            _expect('2 dimensions input', data.shape)
+            raise ValueError(
+                'Expecting 2 dimensional input, got: {shape}'.format(
+                    shape=data.shape))
 
-        if not any(isinstance(data, t) for t in (dd.DataFrame, da.Array)):
+        if not isinstance(data, (dd.DataFrame, da.Array)):
             raise TypeError(_expect((dd.DataFrame, da.Array), type(data)))
-        if not any(
-                isinstance(label, t)
-                for t in (dd.DataFrame, da.Array, dd.Series, type(None))):
+        if not isinstance(label, (dd.DataFrame, da.Array, dd.Series,
+                                  type(None))):
             raise TypeError(
                 _expect((dd.DataFrame, da.Array, dd.Series), type(label)))
 
@@ -158,6 +159,23 @@ class DaskDMatrix:
 
     async def map_local_data(self, client, data, label=None, weights=None):
         '''Obtain references to local data.'''
+
+        def inconsistent(left, left_name, right, right_name):
+            msg = 'Partitions between {a_name} and {b_name} are not ' \
+                'consistent: {a_len} != {b_len}.  ' \
+                'Please try to repartition/rechunk your data.'.format(
+                    a_name=left_name, b_name=right_name, a_len=len(left),
+                    b_len=len(right)
+                )
+            return msg
+
+        def check_columns(parts):
+            # x is required to be 2 dim in __init__
+            assert parts.ndim == 1 or parts.shape[1], 'Data should be' \
+                ' partitioned by row. To avoid this specify the number' \
+                ' of columns for your dask Array explicitly. e.g.' \
+                ' chunks=(partition_size, X.shape[1])'
+
         data = data.persist()
         if label is not None:
             label = label.persist()
@@ -169,28 +187,28 @@ class DaskDMatrix:
         # equivalents.
         X_parts = data.to_delayed()
         if isinstance(X_parts, numpy.ndarray):
-            assert X_parts.shape[1] == 1
+            check_columns(X_parts)
             X_parts = X_parts.flatten().tolist()
 
         if label is not None:
             y_parts = label.to_delayed()
             if isinstance(y_parts, numpy.ndarray):
-                assert y_parts.ndim == 1 or y_parts.shape[1] == 1
+                check_columns(y_parts)
                 y_parts = y_parts.flatten().tolist()
         if weights is not None:
             w_parts = weights.to_delayed()
             if isinstance(w_parts, numpy.ndarray):
-                assert w_parts.ndim == 1 or w_parts.shape[1] == 1
+                check_columns(w_parts)
                 w_parts = w_parts.flatten().tolist()
 
         parts = [X_parts]
         if label is not None:
             assert len(X_parts) == len(
-                y_parts), 'Partitions between X and y are not consistent'
+                y_parts), inconsistent(X_parts, 'X', y_parts, 'labels')
             parts.append(y_parts)
         if weights is not None:
             assert len(X_parts) == len(
-                w_parts), 'Partitions between X and weight are not consistent.'
+                w_parts), inconsistent(X_parts, 'X', w_parts, 'weights')
             parts.append(w_parts)
         parts = list(map(delayed, zip(*parts)))
 
@@ -275,7 +293,11 @@ class DaskDMatrix:
         cols = 0
         for shape in shapes:
             rows += shape[0]
-            cols += shape[1]
+
+            c = shape[1]
+            assert cols in (0, c), 'Shape between partitions are not the' \
+                ' same. Got: {left} and {right}'.format(left=c, right=cols)
+            cols = c
         return (rows, cols)
 
 

src/data/simple_csr_source.cc

@@ -185,7 +185,7 @@ void SimpleCSRSource::CopyFrom(std::string const& cuda_interfaces_str,
                                 cuda_interfaces_str.size()});
   std::vector<Json> const& columns = get<Array>(interfaces);
   size_t n_columns = columns.size();
-  CHECK_GT(n_columns, 0) << "Number of columns must not be greater than 0.";
+  CHECK_GT(n_columns, 0) << "Number of columns must not eqaul to 0.";
 
   auto const& typestr = get<String const>(columns[0]["typestr"]);
   CHECK_EQ(typestr.size(),    3)  << ColumnarErrors::TypestrFormat();

tests/python/test_with_dask.py

@@ -21,12 +21,12 @@ except ImportError:
     pass
 
 kRows = 1000
+kCols = 10
 
 
 def generate_array():
-    n = 10
     partition_size = 20
-    X = da.random.random((kRows, n), partition_size)
+    X = da.random.random((kRows, kCols), partition_size)
     y = da.random.random(kRows, partition_size)
     return X, y
 
@@ -44,7 +44,7 @@ def test_from_dask_dataframe(client):
     prediction = xgb.dask.predict(client, model=booster, data=dtrain)
 
     assert isinstance(prediction, da.Array)
-    assert prediction.shape[0] == kRows, prediction
+    assert prediction.shape[0] == kRows and prediction.shape[1] == kCols
 
     with pytest.raises(ValueError):
         # evals_result is not supported in dask interface.
@@ -59,6 +59,7 @@ def test_from_dask_array(client):
     result = xgb.dask.train(client, {}, dtrain)
 
     prediction = xgb.dask.predict(client, result, dtrain)
+    assert prediction.shape[0] == kRows and prediction.shape[1] == kCols
 
     assert isinstance(prediction, da.Array)
 
@@ -71,6 +72,8 @@ def test_regressor(client):
     regressor.fit(X, y, eval_set=[(X, y)])
     prediction = regressor.predict(X)
 
+    assert prediction.shape[0] == kRows and prediction.shape[1] == kCols
+
     history = regressor.evals_result()
 
     assert isinstance(prediction, da.Array)
@@ -88,6 +91,8 @@ def test_classifier(client):
     classifier.fit(X, y,  eval_set=[(X, y)])
     prediction = classifier.predict(X)
 
+    assert prediction.shape[0] == kRows and prediction.shape[1] == kCols
+
     history = classifier.evals_result()
 
     assert isinstance(prediction, da.Array)