---
title: "subscript(_:)"
framework: createml
role: symbol
role_heading: Instance Subscript
path: "createml/mldatatable/subscript(_:)-3wjk"
---

# subscript(_:)

Retrieves or adds an untyped column with the specified name.

## Declaration

```swift
subscript(columnName: String) -> MLUntypedColumn { get set }
```

## Parameters

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

## Return Value

Return Value A new MLUntypedColumn with the specified name, if it exists; otherwise an invalid column.

## Overview

Overview Use this subscript to retrieve an MLUntypedColumn 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 = table["Distance (AU)"] note: Without a type annotation, the compiler uses this version of subscript(_:) instead of the equivalent subscript(_:) from MLDataColumn. Use the untyped 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 a 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.