Swift MLDataTable - how to remove rows?

Question

I'm creating a MLDataTable from a .csv-file and would like to remove some rows, i.e. all rows where a specific column has a specific value - is this possible?

Answer 1

I know I'm somewhat late with my answer, but hopefully someone else will find it useful.

You can't remove rows from a given table in place, but you can create a new table with some rows filtered out.

Here's an example table:

let employeesDict: [String: MLDataValueConvertible] = [
    "First Name": ["Alice", "Bob", "Charlie", "Dave", "Eva"],
    "Years of experience": [10, 1, 8, 5, 3],
    "Gender": ["female", "male", "male", "male", "female"],
]

let employeesTable = try! MLDataTable(dictionary: employeesDict)

Filtering is achieved by passing an instance of MLDataColumn<Bool> to a table's subscript operator. Apple calls it a 'row mask'. Here's a row mask for filtering out female instances built by hand:

let maleEmployeesMaskByHand = MLDataColumn([false, true, true, true, false])

Passing it as an argument to employeesTable's subscript operator yields the following table:

let maleEmployeesTable = employeesTable[maleEmployeesMaskByHand]
print(maleEmployeesTable)
+----------------+----------------+---------------------+
| Gender         | First Name     | Years of experience |
+----------------+----------------+---------------------+
| male           | Bob            | 1                   |
| male           | Charlie        | 8                   |
| male           | Dave           | 5                   |
+----------------+----------------+---------------------+

Here's another way to build the same row mask:

let genderColumn: MLDataColumn<String> = employeesTable["Gender"]
let maleEmployeesMask = genderColumn != "female"
print(employeesTable[maleEmployeesMask])

First the desired column is retrieved and then – thanks to operator overloading – row mask is built by applying != operator to a whole column.

Here's a way to achieve the same in one line:

print(employeesTable[ employeesTable["Gender"] != "female" ])

A link to relevant documentation: https://developer.apple.com/documentation/createml/mldatatable/3006094-subscript