feat: Converting Pandas DataFrames to Datatables in Python JSON output

py/stencila/schema/util.py

@@ -4,11 +4,54 @@
 import typing
 
 from . import types
-from .types import Node, Entity
+from .types import Node, Entity, Datatable, DatatableColumn, BooleanSchema, IntegerSchema, NumberSchema, StringSchema, \
+    ArraySchema
 
+try:
+    from pandas import DataFrame
+    import numpy
 
-def to_dict(node: Entity) -> dict:
+    pandas_available = True
+except ImportError:
+    class DataFrame:
+        pass
+
+    pandas_available = False
+
+
+def data_frame_to_data_table(df: DataFrame) -> Datatable:
+    columns = []
+
+    for column_name in df.columns:
+        column = df[column_name]
+        values = column.tolist()
+        if column.dtype in (numpy.bool_, numpy.bool8):
+            schema = BooleanSchema()
+            values = [bool(row) for row in values]
+        elif column.dtype in (numpy.int8, numpy.int16, numpy.int32, numpy.int64):
+            schema = IntegerSchema()
+            values = [int(row) for row in values]
+        elif column.dtype in (numpy.float16, numpy.float32, numpy.float64):
+            schema = NumberSchema()
+            values = [float(row) for row in values]
+        elif column.dtype in (numpy.str_, numpy.unicode_,):
+            schema = StringSchema()
+        else:
+            schema = None
+
+        columns.append(
+            DatatableColumn(column_name, values, schema=ArraySchema(items=schema))
+        )
+
+    return Datatable(columns)
+
+
+def to_dict(node: typing.Any) -> dict:
     """Convert an Entity node to a dictionary"""
+    if pandas_available:
+        if isinstance(node, DataFrame):
+            node = data_frame_to_data_table(node)
+
     node_dict = {
         "type": node.__class__.__name__
     }