From b29e6b732d939ce617743ae0ea3cf2ca5008aa0a Mon Sep 17 00:00:00 2001
From: Benjamin Kietzman <bengilgit@gmail.com>
Date: Thu, 5 Sep 2019 17:12:11 -0400
Subject: [PATCH] don't try to dictionary encode dictionary arrays

---
 cpp/src/arrow/python/arrow_to_pandas.cc | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/cpp/src/arrow/python/arrow_to_pandas.cc b/cpp/src/arrow/python/arrow_to_pandas.cc
index a6541ce56e9..2f3f3550ae0 100644
--- a/cpp/src/arrow/python/arrow_to_pandas.cc
+++ b/cpp/src/arrow/python/arrow_to_pandas.cc
@@ -1951,6 +1951,10 @@ Status ConvertTableToPandas(const PandasOptions& options,
     for (int i = 0; i < table->num_columns(); i++) {
       std::shared_ptr<ChunkedArray> col = table->column(i);
       if (categorical_columns.count(table->field(i)->name())) {
+        if (table->field(i)->type()->id() == Type::DICTIONARY) {
+          // this column is already dictionary encoded
+          continue;
+        }
         Datum out;
         RETURN_NOT_OK(DictionaryEncode(&ctx, Datum(col), &out));
         std::shared_ptr<ChunkedArray> array = out.chunked_array();