Add WriteCsv plus unit tests. (#2947)

* Add WriteCsv plus unit tests.

* Add CultureInfo to WriteCsv. Remove index column param. Update unit tests.

* Add CR changes. CultureInfo. Separator.

* Format decimal types individually. Fix culture info. Fix unit tests.

* Format decimal types individually. Fix culture info. Fix unit tests.

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

@@ -4,8 +4,11 @@
 
 using System;
 using System.Collections.Generic;
+using System.Globalization;
 using System.IO;
+using System.Linq;
 using System.Text;
+using Microsoft.ML;
 
 namespace Microsoft.Data.Analysis
 {
@@ -306,5 +309,119 @@ namespace Microsoft.Data.Analysis
                 return ret;
             }
         }
+
+        /// <summary>
+        /// Writes a DataFrame into a CSV.
+        /// </summary>
+        /// <param name="dataFrame"><see cref="DataFrame"/></param>
+        /// <param name="path">CSV file path</param>
+        /// <param name="separator">column separator</param>
+        /// <param name="header">has a header or not</param>
+        /// <param name="encoding">The character encoding. Defaults to UTF8 if not specified</param>
+        /// <param name="cultureInfo">culture info for formatting values</param>
+        public static void WriteCsv(DataFrame dataFrame, string path,
+                                   char separator = ',', bool header = true,
+                                   Encoding encoding = null, CultureInfo cultureInfo = null)
+        {
+            using (FileStream csvStream = new FileStream(path, FileMode.Create))
+            {
+                WriteCsv(dataFrame: dataFrame, csvStream: csvStream,
+                           separator: separator, header: header,
+                           encoding: encoding, cultureInfo: cultureInfo);
+            }
+        }
+
+        /// <summary>
+        /// Writes a DataFrame into a CSV.
+        /// </summary>
+        /// <param name="dataFrame"><see cref="DataFrame"/></param>
+        /// <param name="csvStream">stream of CSV data to be write out</param>
+        /// <param name="separator">column separator</param>
+        /// <param name="header">has a header or not</param>
+        /// <param name="encoding">the character encoding. Defaults to UTF8 if not specified</param>
+        /// <param name="cultureInfo">culture info for formatting values</param>
+        public static void WriteCsv(DataFrame dataFrame, Stream csvStream,
+                           char separator = ',', bool header = true,
+                           Encoding encoding = null, CultureInfo cultureInfo = null)
+        {
+            if (cultureInfo is null)
+            {
+                cultureInfo = CultureInfo.CurrentCulture;
+            }
+
+            if (cultureInfo.NumberFormat.NumberDecimalSeparator.Equals(separator.ToString()))
+            {
+                throw new ArgumentException("Decimal separator cannot match the column separator");
+            }
+
+            if (encoding is null)
+            {
+                encoding = Encoding.ASCII;
+            }
+
+            using (StreamWriter csvFile = new StreamWriter(csvStream, encoding, bufferSize: DefaultStreamReaderBufferSize, leaveOpen: true))
+            {
+                if (dataFrame != null)
+                {
+                    var columnNames = dataFrame.Columns.GetColumnNames();
+
+                    if (header)
+                    {
+                        var headerColumns = string.Join(separator.ToString(), columnNames);
+                        csvFile.WriteLine(headerColumns);
+                    }
+
+                    var record = new StringBuilder();
+
+                    foreach (var row in dataFrame.Rows)
+                    {
+                        bool firstRow = true;
+                        foreach (var cell in row)
+                        {
+                            if (!firstRow)
+                            {
+                                record.Append(separator);
+                            }
+                            else
+                            {
+                                firstRow = false;
+                            }
+
+                            Type t = cell?.GetType();
+
+                            if (t == typeof(bool))
+                            {
+                                record.AppendFormat(cultureInfo, "{0}", cell);
+                                continue;
+                            }
+
+                            if (t == typeof(float))
+                            {
+                                record.AppendFormat(cultureInfo, "{0:G9}", cell);
+                                continue;
+                            }
+
+                            if (t == typeof(double))
+                            {
+                                record.AppendFormat(cultureInfo, "{0:G17}", cell);
+                                continue;
+                            }
+
+                            if (t == typeof(decimal))
+                            {
+                                record.AppendFormat(cultureInfo, "{0:G31}", cell);
+                                continue;
+                            }
+
+                            record.Append(cell);
+                        }
+
+                        csvFile.WriteLine(record);
+
+                        record.Clear();
+                    }
+                }
+            }
+        }
     }
 }

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

@@ -3,7 +3,9 @@
 // See the LICENSE file in the project root for more information.
 
 using System;
+using System.Globalization;
 using System.IO;
+using System.Linq;
 using System.Text;
 using Apache.Arrow;
 using Xunit;
@@ -603,5 +605,160 @@ CMT,1,1,null";
             Assert.Null(df[2, 2]);
             Assert.Null(df[5, 3]);
         }
+
+        [Fact]
+        public void TestWriteCsvWithHeader()
+        {
+            using MemoryStream csvStream = new MemoryStream();
+            DataFrame dataFrame = MakeDataFrameWithAllColumnTypes(10, true);
+
+            DataFrame.WriteCsv(dataFrame, csvStream);
+
+            csvStream.Seek(0, SeekOrigin.Begin);
+            DataFrame readIn = DataFrame.LoadCsv(csvStream);
+
+            Assert.Equal(dataFrame.Rows.Count, readIn.Rows.Count);
+            Assert.Equal(dataFrame.Columns.Count, readIn.Columns.Count);
+            Assert.Equal(1F, readIn[1, 0]);
+            Assert.Equal(1F, readIn[1, 1]);
+            Assert.Equal(1F, readIn[1, 2]);
+            Assert.Equal(1F, readIn[1, 3]);
+            Assert.Equal(1F, readIn[1, 4]);
+            Assert.Equal(1F, readIn[1, 5]);
+            Assert.Equal(1F, readIn[1, 6]);
+            Assert.Equal(1F, readIn[1, 7]);
+            Assert.Equal(1F, readIn[1, 8]);
+            Assert.Equal(1F, readIn[1, 9]);
+            Assert.Equal(1F, readIn[1, 10]);
+        }
+
+        [Fact]
+        public void TestWriteCsvWithCultureInfoRomanianAndSemiColon()
+        {
+            DataFrame dataFrame = MakeDataFrameWithNumericColumns(10, true);
+            dataFrame[1, 1] = 1.1M;
+            dataFrame[1, 2] = 1.2D;
+            dataFrame[1, 3] = 1.3F;
+
+            using MemoryStream csvStream = new MemoryStream();
+            var cultureInfo = new CultureInfo("ro-RO");
+            var separator = ';';
+            DataFrame.WriteCsv(dataFrame, csvStream, separator: separator, cultureInfo: cultureInfo);
+
+            csvStream.Seek(0, SeekOrigin.Begin);
+            DataFrame readIn = DataFrame.LoadCsv(csvStream, separator: separator);
+
+            Assert.Equal(dataFrame.Rows.Count, readIn.Rows.Count);
+            Assert.Equal(dataFrame.Columns.Count, readIn.Columns.Count);
+            Assert.Equal(1F, readIn[1, 0]);
+
+            // LoadCsv does not support culture info, therefore decimal point comma (,) is seen as thousand separator and is ignored when read
+            Assert.Equal(11F, readIn[1, 1]);
+            Assert.Equal(12F, readIn[1, 2]);
+            Assert.Equal(129999992F, readIn[1, 3]);
+
+            Assert.Equal(1F, readIn[1, 4]);
+            Assert.Equal(1F, readIn[1, 5]);
+            Assert.Equal(1F, readIn[1, 6]);
+            Assert.Equal(1F, readIn[1, 7]);
+            Assert.Equal(1F, readIn[1, 8]);
+            Assert.Equal(1F, readIn[1, 9]);
+            Assert.Equal(1F, readIn[1, 10]);
+        }
+
+        [Fact]
+        public void TestWriteCsvWithCultureInfo()
+        {
+            using MemoryStream csvStream = new MemoryStream();
+            DataFrame dataFrame = MakeDataFrameWithNumericColumns(10, true);
+            dataFrame[1, 1] = 1.1M;
+            dataFrame[1, 2] = 1.2D;
+            dataFrame[1, 3] = 1.3F;
+
+            var cultureInfo = new CultureInfo("en-US");
+            DataFrame.WriteCsv(dataFrame, csvStream, cultureInfo: cultureInfo);
+
+            csvStream.Seek(0, SeekOrigin.Begin);
+            DataFrame readIn = DataFrame.LoadCsv(csvStream);
+
+            Assert.Equal(dataFrame.Rows.Count, readIn.Rows.Count);
+            Assert.Equal(dataFrame.Columns.Count, readIn.Columns.Count);
+            Assert.Equal(1F, readIn[1, 0]);
+            Assert.Equal(1.1F, readIn[1, 1]);
+            Assert.Equal(1.2F, readIn[1, 2]);
+            Assert.Equal(1.3F, readIn[1, 3]);
+            Assert.Equal(1F, readIn[1, 4]);
+            Assert.Equal(1F, readIn[1, 5]);
+            Assert.Equal(1F, readIn[1, 6]);
+            Assert.Equal(1F, readIn[1, 7]);
+            Assert.Equal(1F, readIn[1, 8]);
+            Assert.Equal(1F, readIn[1, 9]);
+            Assert.Equal(1F, readIn[1, 10]);
+        }
+
+        [Fact]
+        public void TestWriteCsvWithCultureInfoRomanianAndComma()
+        {
+            using MemoryStream csvStream = new MemoryStream();
+            DataFrame dataFrame = MakeDataFrameWithNumericColumns(10, true);
+
+            var cultureInfo = new CultureInfo("ro-RO");
+            var separator = cultureInfo.NumberFormat.NumberDecimalSeparator.First();
+
+            Assert.Throws<ArgumentException>(() => DataFrame.WriteCsv(dataFrame, csvStream, separator: separator, cultureInfo: cultureInfo));
+        }
+
+        [Fact]
+        public void TestWriteCsvWithNoHeader()
+        {
+            using MemoryStream csvStream = new MemoryStream();
+            DataFrame dataFrame = MakeDataFrameWithAllColumnTypes(10, true);
+
+            DataFrame.WriteCsv(dataFrame, csvStream, header: false);
+
+            csvStream.Seek(0, SeekOrigin.Begin);
+            DataFrame readIn = DataFrame.LoadCsv(csvStream, header: false);
+
+            Assert.Equal(dataFrame.Rows.Count, readIn.Rows.Count);
+            Assert.Equal(dataFrame.Columns.Count, readIn.Columns.Count);
+            Assert.Equal(1F, readIn[1, 0]);
+            Assert.Equal(1F, readIn[1, 1]);
+            Assert.Equal(1F, readIn[1, 2]);
+            Assert.Equal(1F, readIn[1, 3]);
+            Assert.Equal(1F, readIn[1, 4]);
+            Assert.Equal(1F, readIn[1, 5]);
+            Assert.Equal(1F, readIn[1, 6]);
+            Assert.Equal(1F, readIn[1, 7]);
+            Assert.Equal(1F, readIn[1, 8]);
+            Assert.Equal(1F, readIn[1, 9]);
+            Assert.Equal(1F, readIn[1, 10]);
+        }
+
+        [Fact]
+        public void TestWriteCsvWithSemicolonSeparator()
+        {
+            using MemoryStream csvStream = new MemoryStream();
+            DataFrame dataFrame = MakeDataFrameWithAllColumnTypes(10, true);
+
+            var separator = ';';
+            DataFrame.WriteCsv(dataFrame, csvStream, separator: separator);
+
+            csvStream.Seek(0, SeekOrigin.Begin);
+            DataFrame readIn = DataFrame.LoadCsv(csvStream, separator: separator);
+
+            Assert.Equal(dataFrame.Rows.Count, readIn.Rows.Count);
+            Assert.Equal(dataFrame.Columns.Count, readIn.Columns.Count);
+            Assert.Equal(1F, readIn[1, 0]);
+            Assert.Equal(1F, readIn[1, 1]);
+            Assert.Equal(1F, readIn[1, 2]);
+            Assert.Equal(1F, readIn[1, 3]);
+            Assert.Equal(1F, readIn[1, 4]);
+            Assert.Equal(1F, readIn[1, 5]);
+            Assert.Equal(1F, readIn[1, 6]);
+            Assert.Equal(1F, readIn[1, 7]);
+            Assert.Equal(1F, readIn[1, 8]);
+            Assert.Equal(1F, readIn[1, 9]);
+            Assert.Equal(1F, readIn[1, 10]);
+        }
     }
 }