Add type argument for emptyDataFrame()

Author: nikitinas

src/main/kotlin/org/jetbrains/kotlinx/dataframe/api/concat.kt

@@ -48,6 +48,6 @@ public fun <T> Iterable<DataColumn<T>>.concat(): DataColumn<T> {
 }
 
 @JvmName("concatRows")
-public fun <T> Iterable<DataRow<T>?>.concat(): DataFrame<T> = concatImpl(map { it?.toDataFrame() ?: emptyDataFrame(1).cast() })
+public fun <T> Iterable<DataRow<T>?>.concat(): DataFrame<T> = concatImpl(map { it?.toDataFrame() ?: emptyDataFrame(1) })
 
 // endregion

src/main/kotlin/org/jetbrains/kotlinx/dataframe/api/constructors.kt

@@ -271,7 +271,7 @@ public class DataFrameBuilder(private val header: List<String>) {
     public fun randomBoolean(nrow: Int): AnyFrame = fillNotNull(nrow) { Random.nextBoolean() }
 }
 
-public fun emptyDataFrame(nrow: Int = 0): AnyFrame = DataFrame.empty(nrow)
+public fun <T> emptyDataFrame(nrow: Int = 0): DataFrame<T> = DataFrame.empty(nrow).cast()
 
 // endregion
 

src/main/kotlin/org/jetbrains/kotlinx/dataframe/impl/api/concat.kt

@@ -70,7 +70,7 @@ internal fun <T> concatImpl(name: String, columns: List<DataColumn<T>?>, columnS
 
 internal fun <T> concatImpl(dataFrames: List<DataFrame<T>>): DataFrame<T> {
     when (dataFrames.size) {
-        0 -> return emptyDataFrame().cast()
+        0 -> return emptyDataFrame()
         1 -> return dataFrames[0]
     }
 

src/main/kotlin/org/jetbrains/kotlinx/dataframe/impl/api/remove.kt

@@ -5,7 +5,6 @@ import org.jetbrains.kotlinx.dataframe.AnyFrame
 import org.jetbrains.kotlinx.dataframe.ColumnsSelector
 import org.jetbrains.kotlinx.dataframe.DataFrame
 import org.jetbrains.kotlinx.dataframe.api.cast
-import org.jetbrains.kotlinx.dataframe.api.emptyDataFrame
 import org.jetbrains.kotlinx.dataframe.api.name
 import org.jetbrains.kotlinx.dataframe.api.toDataFrame
 import org.jetbrains.kotlinx.dataframe.columns.ColumnGroup
@@ -58,7 +57,7 @@ internal fun <T> DataFrame<T>.removeImpl(allowMissingColumns: Boolean = false, c
         return newCols.toDataFrame()
     }
 
-    val newDf = dfs(columns(), colWithPaths, root) ?: emptyDataFrame(nrow)
+    val newDf = dfs(columns(), colWithPaths, root) ?: DataFrame.empty(nrow)
 
     val removedColumns = root.allRemovedColumns().map { it.pathFromRoot() to it }.sortedBy { originalOrder[it.first] }.map { it.second }
 

src/main/kotlin/org/jetbrains/kotlinx/dataframe/io/common.kt

@@ -3,7 +3,6 @@ package org.jetbrains.kotlinx.dataframe.io
 import com.github.kittinunf.fuel.httpGet
 import org.jetbrains.kotlinx.dataframe.AnyFrame
 import org.jetbrains.kotlinx.dataframe.DataFrame
-import org.jetbrains.kotlinx.dataframe.api.emptyDataFrame
 import org.jetbrains.kotlinx.dataframe.api.toDataFrame
 import org.jetbrains.kotlinx.dataframe.impl.columns.guessColumnType
 import java.io.File
@@ -36,7 +35,7 @@ public fun <T> List<List<T>>.toDataFrame(containsColumns: Boolean = false): AnyF
             guessColumnType(name, values)
         }.toDataFrame()
     }
-    isEmpty() -> emptyDataFrame(0)
+    isEmpty() -> DataFrame.Empty
     else -> {
         val header = get(0).map { it.toString() }
         val data = drop(1)
@@ -50,12 +49,12 @@ public fun <T> List<List<T>>.toDataFrame(containsColumns: Boolean = false): AnyF
     }
 }
 
-internal fun String.isURL(): Boolean = listOf("http:", "https:", "ftp:").any { startsWith(it) }
+public fun isURL(path: String): Boolean = listOf("http:", "https:", "ftp:").any { path.startsWith(it) }
 
-internal fun URL.isFile(): Boolean = protocol == "file"
+public fun isFile(url: URL): Boolean = url.protocol == "file"
 
-internal fun URL.asFileOrNull(): File? = if (isFile()) File(path) else null
+public fun asFileOrNull(url: URL): File? = if (isFile(url)) File(url.path) else null
 
-internal fun URL.asFile(): File = asFileOrNull()!!
+public fun urlAsFile(url: URL): File = File(url.path)
 
-internal fun URL.isProtocolSupported(): Boolean = protocol in setOf("http", "https", "ftp")
+public fun isProtocolSupported(url: URL): Boolean = url.protocol in setOf("http", "https", "ftp")

src/test/kotlin/org/jetbrains/kotlinx/dataframe/api/get.kt

@@ -2,6 +2,7 @@ package org.jetbrains.kotlinx.dataframe.api
 
 import io.kotest.assertions.throwables.shouldThrow
 import io.kotest.matchers.shouldBe
+import org.jetbrains.kotlinx.dataframe.DataFrame
 import org.jetbrains.kotlinx.dataframe.annotations.DataSchema
 import org.junit.Test
 import java.lang.ClassCastException
@@ -11,7 +12,7 @@ class GetTests {
 
     @Test
     fun `exceptions from empty dataframe`() {
-        val empty = emptyDataFrame()
+        val empty = DataFrame.Empty
         shouldThrow<NoSuchElementException> {
             empty.first()
         }

src/test/kotlin/org/jetbrains/kotlinx/dataframe/api/map.kt

@@ -1,13 +1,14 @@
 package org.jetbrains.kotlinx.dataframe.api
 
 import io.kotest.matchers.shouldBe
+import org.jetbrains.kotlinx.dataframe.DataFrame
 import org.junit.Test
 
 class MapTests {
 
     @Test
     fun `map frame column with empty frames`() {
-        val frames by columnOf(dataFrameOf("a")(1), emptyDataFrame(0))
+        val frames by columnOf(dataFrameOf("a")(1), DataFrame.Empty)
         frames.map { it.firstOrNull() }.size() shouldBe frames.size()
     }
 }

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

@@ -518,8 +518,8 @@ class DataFrameTreeTests : BaseTest() {
         val groupCol = grouped.groups.toColumnAccessor()
         val plain = grouped.toDataFrame()
             .update { groupCol }.at(1).withNull()
-            .update { groupCol }.at(2).with { emptyDataFrame(0).cast() }
-            .update { groupCol }.at(3).with { it?.filter { false } }
+            .update { groupCol }.at(2).with { emptyDataFrame() }
+            .update { groupCol }.at(3).with { it.filter { false } }
         val res = plain.explode(dropEmpty = false) { groupCol }
         val expected = plain[groupCol.name()].sumOf { Math.max((it as AnyFrame?)?.nrow ?: 0, 1) }
         res.nrow shouldBe expected