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[//]: # (title: flatten)
<!---IMPORT org.jetbrains.kotlinx.dataframe.samples.api.Modify-->
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.
<!---FUN flatten-->
<tabs>
<tab title="Properties">
```kotlin
// name.firstName -> firstName
// name.lastName -> lastName
df.flatten { name }
```
</tab>
<tab title="Strings">
```kotlin
// name.firstName -> firstName
// name.lastName -> lastName
df.flatten("name")
```
</tab></tabs>
<inline-frame src="resources/org.jetbrains.kotlinx.dataframe.samples.api.Modify.flatten.html" width="100%"/>
<!---END-->
To remove all column groupings in [`DataFrame`](DataFrame.md), invoke `flatten` without parameters:
<!---FUN flattenAll-->
```kotlin
df.flatten()
```
<inline-frame src="resources/org.jetbrains.kotlinx.dataframe.samples.api.Modify.flattenAll.html" width="100%"/>
<!---END-->