---
title: "subscript(_:)"
framework: createml
role: symbol
role_heading: Instance Subscript
path: "createml/mldatatable/subscript(_:)-5tl9r"
---

# subscript(_:)

Retrieves or adds a typed column with the specified name.

## Declaration

```swift
subscript<Element>(columnName: String) -> MLDataColumn<Element> where Element : MLDataValueConvertible { get set }
```

## Parameters

- `columnName`: The name of the column to extract from or add to the data table.

## Return Value

Return Value A new MLDataColumn with the specified name and inferred type, if it exists; otherwise an invalid column.

## Overview

Overview Use this subscript to retrieve an MLDataColumn or add a new one to the data table. important: The number of elements in the column must equal the number of rows in the data table. Otherwise, the data table will be invalidated.

For example, to extract, convert, and add a column as shown above, begin by creating a data table. let data: [String: MLDataValueConvertible] = [     "Planet": ["Mercury", "Venus", "Earth", "Mars", "Jupiter", "Saturn", "Uranus", "Neptune"],     "Distance (AU)": [0.39, 0.72, 1.00, 1.52, 5.20, 9.54, 19.22, 30.06] ]

var table = try MLDataTable(dictionary: data) After creating the table, extract a column. let distanceInAU: MLDataColumn<Double> = table["Distance (AU)"] note: By explicitly adding the type annotation MLDataColumn<Double>, the compiler uses this version of subscript(_:) instead of the equivalent subscript(_:) from MLUntypedColumn. Use the column’s multiplication operator to create a new column of data. // Create a new column of Doubles by multiplying all the the values in // `distanceInAU` by 149,597,870.7 (the number of km in an astronomical unit) let distanceInKm = (distanceInAU * 149_597_870.700) Finally, use the subscript(_:) to add the new column to the table with a different name. table["Distance (km)"] = distanceInKm important: To replace a column, use removeColumn(named:) before adding its replacement. Adding a column with the same name as one already in the data table may invalidate the data table.