public Cursor(InputObjectDataView parent, bool wantsLabel, bool wantsText)
{
Schema = parent.Schema;
_position = -1;
_enumerator = parent._data.GetEnumerator();
_getters = new Delegate[]
{
wantsLabel ? (ValueGetter <bool>)LabelGetterImplementation : null,
wantsText ? (ValueGetter <ReadOnlyMemory <char> >)TextGetterImplementation : null
};
}
public static void Example()
{
// First we create an array of these objects, which we "present" as this IDataView implementation so that it
// can be used in a simple ML.NET pipeline.
var inputArray = new[]
{
new InputObject(false, "Hello my friend."),
new InputObject(true, "Stay awhile and listen."),
new InputObject(true, "Masterfully done hero!")
};
var dataView = new InputObjectDataView(inputArray);
// So, this is a very simple pipeline: a transformer that tokenizes Text, does nothing with the Label column
// at all.
var mlContext = new MLContext();
var transformedDataView = mlContext.Transforms.Text.TokenizeIntoWords(
"TokenizedText", "Text").Fit(dataView).Transform(dataView);
var textColumn = transformedDataView.Schema["Text"];
var tokensColumn = transformedDataView.Schema["TokenizedText"];
using (var cursor = transformedDataView.GetRowCursor(new[] { textColumn, tokensColumn }))
{
// Note that it is best to get the getters and values *before* iteration, so as to faciliate buffer
// sharing (if applicable), and column-type validation once, rather than many times.
ReadOnlyMemory <char> textValue = default;
VBuffer <ReadOnlyMemory <char> > tokensValue = default;
var textGetter = cursor.GetGetter <ReadOnlyMemory <char> >(textColumn);
var tokensGetter = cursor.GetGetter <VBuffer <ReadOnlyMemory <char> > >(tokensColumn);
while (cursor.MoveNext())
{
textGetter(ref textValue);
tokensGetter(ref tokensValue);
Console.WriteLine($"{textValue} => {string.Join(", ", tokensValue.DenseValues())}");
}
// The output to console is this:
// Hello my friend. => Hello, my, friend.
// Stay awhile and listen. => Stay, awhile, and, listen.
// Masterfully done hero! => Masterfully, done, hero!
// Note that it may be interesting to set a breakpoint on the Console.WriteLine, and explore
// what is going on with the cursor, and the buffers. In particular, on the third iteration,
// while `tokensValue` is logically presented as a three element array, internally you will
// see that the arrays internal to that structure have (at least) four items, specifically:
// `Masterfully`, `done`, `hero!`, `listen.`. In this way we see a simple example of the details
// of how buffer sharing from one iteration to the next actually works.
}
}
