Allow for changes in dictionary while reading a row-group column (#367)

fastparquet/core.py

@@ -227,6 +227,15 @@ def read_col(column, schema_helper, infile, use_cat=False,
     num = 0
     row_idx = 0
     while True:
+        if ph.type == parquet_thrift.PageType.DICTIONARY_PAGE:
+            dic2 = np.array(read_dictionary_page(infile, schema_helper, ph, cmd))
+            dic2 = convert(dic2, se)
+            if use_cat and (dic2 != dic).any():
+                raise RuntimeError("Attempt to read as categorical a column"
+                                   "with multiple dictionary pages.")
+            dic = dic2
+            ph = read_thrift(infile, parquet_thrift.PageHeader)
+            continue
         if (selfmade and hasattr(cmd, 'statistics') and
                 getattr(cmd.statistics, 'null_count', 1) == 0):
             skip_nulls = True