/// <summary>
/// Configures a reader for text files.
/// </summary>
/// <typeparam name="TShape">The type shape parameter, which must be a valid-schema shape. As a practical
/// matter this is generally not explicitly defined from the user, but is instead inferred from the return
/// type of the <paramref name="func"/> where one takes an input <see cref="Context"/> and uses it to compose
/// a shape-type instance describing what the columns are and how to load them from the file.</typeparam>
/// <param name="env">The environment.</param>
/// <param name="func">The delegate that describes what fields to read from the text file, as well as
/// describing their input type. The way in which it works is that the delegate is fed a <see cref="Context"/>,
/// and the user composes a shape type with <see cref="PipelineColumn"/> instances out of that <see cref="Context"/>.
/// The resulting data will have columns with the names corresponding to their names in the shape type.</param>
/// <param name="files">Input files. If <c>null</c> then no files are read, but this means that options or
/// configurations that require input data for initialization (for example, <paramref name="hasHeader"/> or
/// <see cref="Context.LoadFloat(int, int?)"/>) with a <c>null</c> second argument.</param>
/// <param name="hasHeader">Data file has header with feature names.</param>
/// <param name="separator">Text field separator.</param>
/// <param name="allowQuoting">Whether the input -may include quoted values, which can contain separator
/// characters, colons, and distinguish empty values from missing values. When true, consecutive separators
/// denote a missing value and an empty value is denoted by <c>""</c>. When false, consecutive separators
/// denote an empty value.</param>
/// <param name="allowSparse">Whether the input may include sparse representations.</param>
/// <param name="trimWhitspace">Remove trailing whitespace from lines.</param>
/// <returns>A configured statically-typed reader for text files.</returns>
public static DataReader <IMultiStreamSource, TShape> CreateReader <[IsShape] TShape>(
IHostEnvironment env, Func <Context, TShape> func, IMultiStreamSource files = null,
bool hasHeader = false, char separator = '\t', bool allowQuoting = true, bool allowSparse = true,
bool trimWhitspace = false)
{
Contracts.CheckValue(env, nameof(env));
env.CheckValue(func, nameof(func));
env.CheckValueOrNull(files);
// Populate all args except the columns.
var args = new Arguments();
args.AllowQuoting = allowQuoting;
args.AllowSparse = allowSparse;
args.HasHeader = hasHeader;
args.SeparatorChars = new[] { separator };
args.TrimWhitespace = trimWhitspace;
var rec = new TextReconciler(args, files);
var ctx = new Context(rec);
using (var ch = env.Start("Initializing " + nameof(TextLoader)))
{
var readerEst = StaticPipeUtils.ReaderEstimatorAnalyzerHelper(env, ch, ctx, rec, func);
Contracts.AssertValue(readerEst);
return(readerEst.Fit(files));
}
}
