subscript(_:)

Declaration

subscript(mask: MLDataColumn<Bool>) -> MLDataTable { get }

Parameters

• mask:

  A Boolean column indicating whether rows should be kept (true) or removed (false) in the derived table.

Return Value

A new data table.

Overview

Use this Boolean column–based subscript to create a new table by masking a subset of the table rows.

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For example, to filter the values in a data table as shown above, begin by creating a table with the original data.

let data: [String: MLDataValueConvertible] = [
    "Title": ["Alice in Wonderland", "Hamlet", "Treasure Island", "Peter Pan"],
    "Genre": ["Fantasy", "Drama", "Adventure", "Fantasy"]
]

let table = try? MLDataTable(dictionary: data) else {
    fatalError("Invalid dictionary data")
}

After you create the table, use column arithmetic operators or the map(_:) method to build a row mask. The subscript uses the Boolean values in the row mask to determine whether to keep a row.

// Retrieve the "Genre" column from the table.
guard let genreColumn = table["Genre", String.self] else {
    fatalError("Missing or invalid 'genre' column in table.")
}

// Create a new column of Booleans by comparing all of the values
// in `Genre` with `Fantasy` using the
// `!=(MLDataColumn<String>, String) -> MLDataColumn<Bool>` operator.
let noFantasyMask = genreColumn != "Fantasy"

Use subscript(mask: MLDataColumn<Bool>) with the Boolean column–row mask to create a filtered table.

let noFantasyTable = table[noFantasyMask]