init research

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+[//]: # (title: getColumn)
+
+<!---IMPORT org.jetbrains.kotlinx.dataframe.samples.api.Access-->
+
+Return column by column name or [column selector](ColumnSelectors.md) as [`DataColumn`](DataColumn.md). Throws exception if requested column doesn't exist.
+
+<!---FUN getColumn-->
+<tabs>
+<tab title="Properties">
+
+```kotlin
+df.getColumn { age }
+```
+
+</tab>
+<tab title="Strings">
+
+```kotlin
+df.getColumn("age")
+```
+
+</tab></tabs>
+<!---END-->
+
+## getColumnOrNull
+
+Return top-level column by column name or [column selector](ColumnSelectors.md) as [`DataColumn`](DataColumn.md) or null if requested column doesn't exist.
+
+<!---FUN getColumnOrNull-->
+<tabs>
+<tab title="Properties">
+
+```kotlin
+df.getColumnOrNull { age }
+```
+
+</tab>
+<tab title="Strings">
+
+```kotlin
+df.getColumnOrNull("age")
+```
+
+</tab></tabs>
+<!---END-->
+
+## getColumnGroup
+
+Return top-level column by column name or [column selector](ColumnSelectors.md) as [`ColumnGroup`](DataColumn.md#columngroup). Throws exception if requested column doesn't exist or is not a `ColumnGroup`.
+
+<!---FUN getColumnGroup-->
+<tabs>
+<tab title="Properties">
+
+```kotlin
+df.getColumnGroup { name }
+```
+
+</tab>
+<tab title="Strings">
+
+```kotlin
+df.getColumnGroup("name")
+```
+
+</tab></tabs>
+<!---END-->
+
+## getColumns
+
+Return list of selected columns.
+
+<!---FUN getColumns-->
+<tabs>
+<tab title="Properties">
+
+```kotlin
+df.getColumns { age and name }
+```
+
+</tab>
+<tab title="Strings">
+
+```kotlin
+df.getColumns("age", "name")
+```
+
+</tab></tabs>
+<!---END-->