[//]: # (title: flatten)
Returns [`DataFrame`](DataFrame.md) without column groupings under selected columns.
```text
flatten [ { columns } ]
```
Columns will keep their original names after flattening.
Potential column name clashes are resolved by adding minimal possible name prefix from ancestor columns.
**Related operations**: [](groupUngroupFlatten.md)
See [column selectors](ColumnSelectors.md) for how to select the columns for this operation.
```kotlin
// name.firstName -> firstName
// name.lastName -> lastName
df.flatten { name }
```
```kotlin
// name.firstName -> firstName
// name.lastName -> lastName
df.flatten("name")
```
To remove all column groupings in [`DataFrame`](DataFrame.md), invoke `flatten` without parameters:
```kotlin
df.flatten()
```