fixed tests aside from the compiler plugin

Author: Jolanrensen

core/api/core.api

@@ -3,7 +3,6 @@ package org.jetbrains.kotlinx.dataframe.math
 import org.jetbrains.kotlinx.dataframe.api.isNaN
 import org.jetbrains.kotlinx.dataframe.impl.IsBetterThan
 import org.jetbrains.kotlinx.dataframe.impl.aggregation.aggregators.CalculateReturnType
-import org.jetbrains.kotlinx.dataframe.impl.aggregation.aggregators.preserveReturnTypeNullIfEmpty
 import org.jetbrains.kotlinx.dataframe.impl.bestByOrNull
 import org.jetbrains.kotlinx.dataframe.impl.bestNotNaByOrNull
 import org.jetbrains.kotlinx.dataframe.impl.canBeNaN

core/src/main/kotlin/org/jetbrains/kotlinx/dataframe/math/minMax.kt

@@ -66,7 +66,7 @@ class DescribeTests {
             std.shouldBeNaN()
             min.isNaN shouldBe true
             p25 shouldBe 1.75
-            median shouldBe 3.0
+            median.isNaN shouldBe true
             p75.isNaN shouldBe true
             max.isNaN shouldBe true
         }

core/src/test/kotlin/org/jetbrains/kotlinx/dataframe/api/describe.kt

@@ -153,52 +153,52 @@ class StatisticsTests {
             "yearsToRetirement",
         )
 
-        val median01 = res0["age"][0] as Int
-        median01 shouldBe 22
+        val median01 = res0["age"][0] as Double
+        median01 shouldBe 22.0
         // val median02 = res0["weight"][0] as Double
         // median02 shouldBe 66.0
 
         // scenario #1: particular column
         val res1 = personsDf.groupBy("city").medianFor("age")
         res1.columnNames() shouldBe listOf("city", "age")
 
-        val median11 = res1["age"][0] as Int
-        median11 shouldBe 22
+        val median11 = res1["age"][0] as Double
+        median11 shouldBe 22.0
 
         // scenario #1.1: particular column via median
         val res11 = personsDf.groupBy("city").median("age")
         res11.columnNames() shouldBe listOf("city", "age")
 
-        val median111 = res11["age"][0] as Int
-        median111 shouldBe 22
+        val median111 = res11["age"][0] as Double
+        median111 shouldBe 22.0
 
         // scenario #2: particular column with new name - schema changes
         val res2 = personsDf.groupBy("city").median("age", name = "newAge")
         res2.columnNames() shouldBe listOf("city", "newAge")
 
-        val median21 = res2["newAge"][0] as Int
-        median21 shouldBe 22
+        val median21 = res2["newAge"][0] as Double
+        median21 shouldBe 22.0
 
         // scenario #2.1: particular column with new name - schema changes but via columnSelector
         val res21 = personsDf.groupBy("city").median(name = "newAge") { "age"<Int>() }
         res21.columnNames() shouldBe listOf("city", "newAge")
 
-        val median211 = res21["newAge"][0] as Int
-        median211 shouldBe 22
+        val median211 = res21["newAge"][0] as Double
+        median211 shouldBe 22.0
 
         // scenario #2.2: two columns with new name - schema changes but via columnSelector
         val res22 = personsDf.groupBy("city").median(name = "newAge") { "age"<Int>() and "yearsToRetirement"<Int>() }
         res22.columnNames() shouldBe listOf("city", "newAge")
 
-        val median221 = res22["newAge"][0] as Int
-        median221 shouldBe 32
+        val median221 = res22["newAge"][0] as Double
+        median221 shouldBe 32.5
 
         // scenario #3: create new column via expression
         val res3 = personsDf.groupBy("city").medianOf(name = "newAge") { "age"<Int>() * 10 }
         res3.columnNames() shouldBe listOf("city", "newAge")
 
-        val median31 = res3["newAge"][0] as Int
-        median31 shouldBe 220
+        val median31 = res3["newAge"][0] as Double
+        median31 shouldBe 220.0
 
         // scenario #3.1: create new column via expression with Double
         val res31 = personsDf.groupBy("city").medianOf(name = "newAge") { "weight"<Double>() * 10 }

core/src/test/kotlin/org/jetbrains/kotlinx/dataframe/api/statistics.kt

@@ -738,7 +738,7 @@ class DataFrameTests : BaseTest() {
             this["name"].toList() shouldBe listOf("Alice", "Bob", "Charlie")
             this["n"].toList() shouldBe listOf(2, 2, 3)
             this["old count"].toList() shouldBe listOf(0, 2, 2)
-            this["median age"].toList() shouldBe listOf(17, 37, 30)
+            this["median age"].toList() shouldBe listOf(17.5, 37.5, 30.0)
             this["min age"].toList() shouldBe listOf(15, 30, 20)
             this["oldest origin"].toList() shouldBe listOf(null, "Dubai", "Milan")
             this["youngest origin"].toList() shouldBe listOf("London", "Tokyo", "Moscow")

core/src/test/kotlin/org/jetbrains/kotlinx/dataframe/testSets/person/DataFrameTests.kt

@@ -814,7 +814,7 @@ class DataFrameTreeTests : BaseTest() {
             .groupBy { expr { age > 30 } into "isOld" }.into(group)
             .aggregate {
                 group().maxBy { rowsCount() }.weight.median() into "m"
-            }["m"] shouldBe 61
+            }["m"] shouldBe 61.5
     }
 
     @Test