Fix DataFrame.LoadCsv can not load CSV with duplicate column names

Author: asmirnov82

src/Microsoft.Data.Analysis/DataFrame.IO.cs

@@ -8,6 +8,7 @@
 using System.Data.Common;
 using System.Globalization;
 using System.IO;
+using System.Linq;
 using System.Text;
 using System.Threading.Tasks;
 
@@ -349,8 +350,8 @@ private static DataFrameColumn CreateColumn(Type kind, string[] columnNames, int
         private static DataFrame ReadCsvLinesIntoDataFrame(WrappedStreamReaderOrStringReader wrappedReader,
                                 char separator = ',', bool header = true,
                                 string[] columnNames = null, Type[] dataTypes = null,
-                                long numberOfRowsToRead = -1, int guessRows = 10, bool addIndexColumn = false
-                                )
+                                long numberOfRowsToRead = -1, int guessRows = 10, bool addIndexColumn = false,
+                                bool renameDuplicatedColumns = false)
         {
             if (dataTypes == null && guessRows <= 0)
             {
@@ -376,6 +377,25 @@ private static DataFrame ReadCsvLinesIntoDataFrame(WrappedStreamReaderOrStringRe
                 // First pass: schema and number of rows.
                 while ((fields = parser.ReadFields()) != null)
                 {
+                    if (renameDuplicatedColumns)
+                    {
+                        var names = new Dictionary<string, int>();
+
+                        for (int i = 0; i < fields.Length; i++)
+                        {
+                            if (names.TryGetValue(fields[i], out int index))
+                            {
+                                var newName = String.Format("{0}.{1}", fields[i], index);
+                                names[fields[i]] = ++index;
+                                fields[i] = newName;
+                            }
+                            else
+                            {
+                                names.Add(fields[i], 1);
+                            }
+                        }
+                    }
+
                     if ((numberOfRowsToRead == -1) || rowline < numberOfRowsToRead)
                     {
                         if (linesForGuessType.Count < guessRows || (header && rowline == 0))
@@ -525,12 +545,13 @@ public static DataFrame LoadCsvFromString(string csvString,
         /// <param name="guessRows">number of rows used to guess types</param>
         /// <param name="addIndexColumn">add one column with the row index</param>
         /// <param name="encoding">The character encoding. Defaults to UTF8 if not specified</param>
+        /// <param name="renameDuplicatedColumns">If set to true, columns with repeated names are auto-renamed.</param>
         /// <returns><see cref="DataFrame"/></returns>
         public static DataFrame LoadCsv(Stream csvStream,
                                 char separator = ',', bool header = true,
                                 string[] columnNames = null, Type[] dataTypes = null,
                                 long numberOfRowsToRead = -1, int guessRows = 10, bool addIndexColumn = false,
-                                Encoding encoding = null)
+                                Encoding encoding = null, bool renameDuplicatedColumns = false)
         {
             if (!csvStream.CanSeek)
             {
@@ -543,7 +564,7 @@ public static DataFrame LoadCsv(Stream csvStream,
             }
 
             WrappedStreamReaderOrStringReader wrappedStreamReaderOrStringReader = new WrappedStreamReaderOrStringReader(csvStream, encoding ?? Encoding.UTF8);
-            return ReadCsvLinesIntoDataFrame(wrappedStreamReaderOrStringReader, separator, header, columnNames, dataTypes, numberOfRowsToRead, guessRows, addIndexColumn);
+            return ReadCsvLinesIntoDataFrame(wrappedStreamReaderOrStringReader, separator, header, columnNames, dataTypes, numberOfRowsToRead, guessRows, addIndexColumn, renameDuplicatedColumns);
         }
 
         /// <summary>

test/Microsoft.Data.Analysis.Tests/DataFrame.IOTests.cs

@@ -154,6 +154,46 @@ void ReducedRowsTest(DataFrame reducedRows)
             ReducedRowsTest(csvDf);
         }
 
+        [Fact]
+        public void TestReadCsvWithHeaderAndDuplicatedColumns_WithoutRenaming()
+        {
+
+            string data = @$"vendor_id,rate_code,passenger_count,trip_time_in_secs,trip_distance,payment_type,payment_type,fare_amount
+CMT,1,1,1271,3.8,CRD,CRD,17.5
+CMT,1,1,474,1.5,CRD,CRD,8
+CMT,1,1,637,1.4,CRD,CRD,8.5
+CMT,1,1,181,0.6,CSH,CSH,4.5";
+
+            Assert.Throws<System.ArgumentException>(() => DataFrame.LoadCsv(GetStream(data)));
+        }
+
+        [Fact]
+        public void TestReadCsvWithHeaderAndDuplicatedColumns_WithDuplicateColumnRenaming()
+        {
+
+            string data = @$"vendor_id,rate_code,passenger_count,trip_time_in_secs,trip_distance,payment_type,payment_type,payment_type,fare_amount
+CMT,1,1,1271,3.8,CRD,CRD_1,Test,17.5
+CMT,1,1,474,1.5,CRD,CRD,Test,8
+CMT,1,1,637,1.4,CRD,CRD,Test,8.5
+CMT,1,1,181,0.6,CSH,CSH,Test,4.5";
+
+            DataFrame df = DataFrame.LoadCsv(GetStream(data), renameDuplicatedColumns: true);
+
+            Assert.Equal(4, df.Rows.Count);
+            Assert.Equal(9, df.Columns.Count);
+            Assert.Equal("CMT", df.Columns["vendor_id"][3]);
+
+            Assert.Equal("payment_type", df.Columns[5].Name);
+            Assert.Equal("payment_type.1", df.Columns[6].Name);
+            Assert.Equal("payment_type.2", df.Columns[7].Name);
+
+            Assert.Equal("CRD", df.Columns["payment_type"][0]);
+            Assert.Equal("CRD_1", df.Columns["payment_type.1"][0]);
+            Assert.Equal("Test", df.Columns["payment_type.2"][0]);
+
+            VerifyColumnTypes(df);
+        }
+
         [Fact]
         public void TestReadCsvSplitAcrossMultipleLines()
         {