init research

dataframe/docs/StardustDocs/topics/distinct.md

@@ -0,0 +1,73 @@
+[//]: # (title: distinct)
+
+<!---IMPORT org.jetbrains.kotlinx.dataframe.samples.api.Access-->
+
+Removes duplicate rows.
+The rows in the resulting [`DataFrame`](DataFrame.md) are in the same order as they were in the original [`DataFrame`](DataFrame.md).
+
+Related operations: [](filterRows.md)
+
+<!---FUN distinct-->
+
+```kotlin
+df.distinct()
+```
+
+<inline-frame src="resources/org.jetbrains.kotlinx.dataframe.samples.api.Access.distinct.html" width="100%"/>
+<!---END-->
+
+If columns are specified, resulting [`DataFrame`](DataFrame.md) will have only given columns with distinct values.
+
+See [column selectors](ColumnSelectors.md) for how to select the columns for this operation.
+
+<!---FUN distinctColumns-->
+<tabs>
+<tab title="Properties">
+
+```kotlin
+df.distinct { age and name }
+// same as
+df.select { age and name }.distinct()
+```
+
+</tab>
+<tab title="Strings">
+
+```kotlin
+df.distinct("age", "name")
+// same as
+df.select("age", "name").distinct()
+```
+
+</tab></tabs>
+<inline-frame src="resources/org.jetbrains.kotlinx.dataframe.samples.api.Access.distinctColumns.html" width="100%"/>
+<!---END-->
+
+## distinctBy
+
+Keep only the first row for every group of rows grouped by some condition.
+
+See [column selectors](ColumnSelectors.md) for how to select the columns for this operation.
+
+<!---FUN distinctBy-->
+<tabs>
+<tab title="Properties">
+
+```kotlin
+df.distinctBy { age and name }
+// same as
+df.groupBy { age and name }.mapToRows { group.first() }
+```
+
+</tab>
+<tab title="Strings">
+
+```kotlin
+df.distinctBy("age", "name")
+// same as
+df.groupBy("age", "name").mapToRows { group.first() }
+```
+
+</tab></tabs>
+<inline-frame src="resources/org.jetbrains.kotlinx.dataframe.samples.api.Access.distinctBy.html" width="100%"/>
+<!---END-->