init research

dataframe/plugins/kotlin-dataframe/testData/box/csDsl/select.kt

@@ -0,0 +1,15 @@
+import org.jetbrains.kotlinx.dataframe.*
+import org.jetbrains.kotlinx.dataframe.annotations.*
+import org.jetbrains.kotlinx.dataframe.api.*
+import org.jetbrains.kotlinx.dataframe.io.*
+
+fun box(): String {
+    val df = dataFrameOf(
+        "a" to listOf(1),
+        "b" to listOf(1),
+    ).group { a and b }.into("gr")
+    val res = df.select { gr.select { a and b } }
+    res.a
+    res.b
+    return "OK"
+}