How to add calculated column into IDataView, and then included as a feature - ml.net

Question

I have some data in a csv file:
Survived Pclass Sex Age
0 3 male 22
1 1 female 38
1 3 male 26
1 1 female 35
...
I loaded the data using:
context.Data.LoadFromTextFile(path: dataPath,...);
Once I loaded the data, I need to add calculated column say, AgeName, so that the:
if (Age < 18)
AgeName ="Child"
else if(Age < 55)
AgeNAme = "Man"
else
AgeNAme = "Grandpa"
Is there builtin method in the ML.NET in order to add the column, or do I need to implement it manually?

Answer 1

I think you would want to use the CustomMapping transform.
Below is a sample. First, some input and output classes:
class InputData
{
public int Age { get; set; }
}
class CustomMappingOutput
{
public string AgeName { get; set; }
}
class TransformedData
{
public int Age { get; set; }
public string AgeName { get; set; }
}
Then, in the ML.NET program:
MLContext mlContext = new MLContext();
var samples = new List<InputData>
{
new InputData { Age = 16 },
new InputData { Age = 35 },
new InputData { Age = 60 },
new InputData { Age = 28 },
};
var data = mlContext.Data.LoadFromEnumerable(samples);
Action<InputData, CustomMappingOutput> mapping =
(input, output) =>
{
if (input.Age < 18)
{
output.AgeName = "Child";
}
else if (input.Age < 55)
{
output.AgeName = "Man";
}
else
{
output.AgeName = "Grandpa";
}
};
var pipeline = mlContext.Transforms.CustomMapping(mapping, contractName: null);
var transformer = pipeline.Fit(data);
var transformedData = transformer.Transform(data);
var dataEnumerable = mlContext.Data.CreateEnumerable<TransformedData>(transformedData, reuseRowObject: true);
foreach (var row in dataEnumerable)
{
Console.WriteLine($"{row.Age}\t {row.AgeName}");
}