Handling Chars as Strings implicitly

core/api/core.api

@@ -6501,8 +6501,12 @@ public final class org/jetbrains/kotlinx/dataframe/api/ParseKt {
 	public static synthetic fun parse$default (Lorg/jetbrains/kotlinx/dataframe/DataFrame;[Lorg/jetbrains/kotlinx/dataframe/columns/ColumnReference;Lorg/jetbrains/kotlinx/dataframe/api/ParserOptions;ILjava/lang/Object;)Lorg/jetbrains/kotlinx/dataframe/DataFrame;
 	public static final fun parseAnyFrameNullable (Lorg/jetbrains/kotlinx/dataframe/DataColumn;Lorg/jetbrains/kotlinx/dataframe/api/ParserOptions;)Lorg/jetbrains/kotlinx/dataframe/DataColumn;
 	public static synthetic fun parseAnyFrameNullable$default (Lorg/jetbrains/kotlinx/dataframe/DataColumn;Lorg/jetbrains/kotlinx/dataframe/api/ParserOptions;ILjava/lang/Object;)Lorg/jetbrains/kotlinx/dataframe/DataColumn;
+	public static final fun parseChar (Lorg/jetbrains/kotlinx/dataframe/DataColumn;Lorg/jetbrains/kotlinx/dataframe/api/ParserOptions;)Lorg/jetbrains/kotlinx/dataframe/DataColumn;
+	public static synthetic fun parseChar$default (Lorg/jetbrains/kotlinx/dataframe/DataColumn;Lorg/jetbrains/kotlinx/dataframe/api/ParserOptions;ILjava/lang/Object;)Lorg/jetbrains/kotlinx/dataframe/DataColumn;
 	public static final fun tryParse (Lorg/jetbrains/kotlinx/dataframe/DataColumn;Lorg/jetbrains/kotlinx/dataframe/api/ParserOptions;)Lorg/jetbrains/kotlinx/dataframe/DataColumn;
 	public static synthetic fun tryParse$default (Lorg/jetbrains/kotlinx/dataframe/DataColumn;Lorg/jetbrains/kotlinx/dataframe/api/ParserOptions;ILjava/lang/Object;)Lorg/jetbrains/kotlinx/dataframe/DataColumn;
+	public static final fun tryParseChar (Lorg/jetbrains/kotlinx/dataframe/DataColumn;Lorg/jetbrains/kotlinx/dataframe/api/ParserOptions;)Lorg/jetbrains/kotlinx/dataframe/DataColumn;
+	public static synthetic fun tryParseChar$default (Lorg/jetbrains/kotlinx/dataframe/DataColumn;Lorg/jetbrains/kotlinx/dataframe/api/ParserOptions;ILjava/lang/Object;)Lorg/jetbrains/kotlinx/dataframe/DataColumn;
 }
 
 public final class org/jetbrains/kotlinx/dataframe/api/ParserOptions {

core/src/main/kotlin/org/jetbrains/kotlinx/dataframe/api/convertTo.kt

@@ -52,7 +52,7 @@ public class ConverterScope(public val fromType: KType, public val toSchema: Col
  * df.convertTo<SomeSchema> {
  *     // defines how to convert Int? -> String
  *     convert<Int?>().with { it?.toString() ?: "No input given" }
- *     // defines how to convert String -> SomeType
+ *     // defines how to convert String -> SomeType (and Char.toString() -> SomeType)
  *     parser { SomeType(it) }
  *     // fill missing column `sum` with expression `a+b`
  *     fill { sum }.with { a + b }
@@ -102,6 +102,10 @@ public fun <T, C> ConvertToFill<T, C>.with(expr: RowExpression<T, C>) {
 
 /**
  * Defines how to convert `String` values into given type [C].
+ *
+ * This method is a shortcut for `convert<String>().with { }`.
+ *
+ * If no converter is defined for `Char` values, this converter will be used for them as well.
  */
 public inline fun <reified C> ConvertSchemaDsl<*>.parser(noinline parser: (String) -> C): Unit =
     convert<String>().with(parser)

core/src/main/kotlin/org/jetbrains/kotlinx/dataframe/api/parse.kt

@@ -18,6 +18,7 @@ import java.time.format.DateTimeFormatter
 import java.util.Locale
 import kotlin.reflect.KProperty
 import kotlin.reflect.KType
+import kotlin.reflect.typeOf
 
 /**
  * ### Global Parser Options
@@ -197,6 +198,28 @@ public class ParserOptions(
 /** @include [tryParseImpl] */
 public fun DataColumn<String?>.tryParse(options: ParserOptions? = null): DataColumn<*> = tryParseImpl(options)
 
+/**
+ * Tries to parse a column of chars into a column of a different type.
+ * Each parser in [Parsers] is run in order until a valid parser is found,
+ * a.k.a. that parser was able to parse all values in the column successfully. If a parser
+ * fails to parse any value, the next parser is tried. If all the others fail, the final parser
+ * returns strings.
+ *
+ * Parsers that are [covered by][StringParser.coveredBy] other parsers are skipped.
+ *
+ * @param options options for parsing, like providing a locale or a custom date-time formatter
+ * @throws IllegalStateException if no valid parser is found (unlikely, unless the `String` parser is disabled)
+ * @return a new column with parsed values
+ */
+@JvmName("tryParseChar")
+public fun DataColumn<Char?>.tryParse(options: ParserOptions? = null): DataColumn<*> {
+    // skip the Char parser, as we're trying to parse away from Char
+    val providedSkipTypes = options?.skipTypes ?: DataFrame.parser.skipTypes
+    val parserOptions = (options ?: ParserOptions()).copy(skipTypes = providedSkipTypes + typeOf<Char>())
+
+    return map { it?.toString() }.tryParse(parserOptions)
+}
+
 public fun <T> DataFrame<T>.parse(options: ParserOptions? = null): DataFrame<T> =
     parse(options) {
         colsAtAnyDepth { !it.isColumnGroup() }
@@ -220,6 +243,23 @@ public fun <T> DataFrame<T>.parse(options: ParserOptions? = null): DataFrame<T>
 public fun DataColumn<String?>.parse(options: ParserOptions? = null): DataColumn<*> =
     tryParse(options).also { if (it.typeClass == String::class) error("Can't guess column type") }
 
+/**
+ * Tries to parse a column of chars as strings into a column of a different type.
+ * Each parser in [Parsers] is run in order until a valid parser is found,
+ * a.k.a. that parser was able to parse all values in the column successfully. If a parser
+ * fails to parse any value, the next parser is tried.
+ *
+ * If all fail, the column is returned as `String`, this can never fail.
+ *
+ * Parsers that are [covered by][StringParser.coveredBy] other parsers are skipped.
+ *
+ * @param options options for parsing, like providing a locale or a custom date-time formatter
+ * @return a new column with parsed values
+ */
+@JvmName("parseChar")
+public fun DataColumn<Char?>.parse(options: ParserOptions? = null): DataColumn<*> =
+    tryParse(options) // no need to throw an exception, as Char can always be parsed as String
+
 @JvmName("parseAnyFrameNullable")
 public fun DataColumn<AnyFrame?>.parse(options: ParserOptions? = null): DataColumn<AnyFrame?> =
     map { it?.parse(options) }

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

@@ -367,7 +367,13 @@ internal fun createConverter(from: KType, to: KType, options: ParserOptions? = n
 
             Char::class -> when (toClass) {
                 Int::class -> convert<Char> { it.code }
-                else -> null
+
+                else -> // convert char to string and then to target type
+                    getConverter(typeOf<String>(), to, options)?.let { stringConverter ->
+                        convert<Char> {
+                            stringConverter(it.toString())
+                        }
+                    }
             }
 
             Int::class -> when (toClass) {

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

@@ -45,8 +45,10 @@ import org.jetbrains.kotlinx.dataframe.schema.ColumnSchema
 import org.jetbrains.kotlinx.dataframe.schema.DataFrameSchema
 import org.jetbrains.kotlinx.dataframe.size
 import kotlin.reflect.KType
+import kotlin.reflect.full.isSubtypeOf
 import kotlin.reflect.full.withNullability
 import kotlin.reflect.jvm.jvmErasure
+import kotlin.reflect.typeOf
 
 private val logger = KotlinLogging.logger {}
 
@@ -143,7 +145,22 @@ internal fun AnyFrame.convertToImpl(
                         // try to perform any user-specified conversions first
                         val from = originalColumn.type()
                         val to = targetSchema.type
-                        val converter = dsl.getConverter(from, targetSchema)
+                        var converter = dsl.getConverter(from, targetSchema)
+
+                        // special case for Char columns; check if we have any converters for String -> target
+                        // if so, we can convert Char -> String -> target
+                        if (converter == null && from.isSubtypeOf(typeOf<Char?>())) {
+                            val stringConverter = dsl.getConverter(
+                                fromType = typeOf<String>().withNullability(from.isMarkedNullable),
+                                toSchema = targetSchema,
+                            )
+                            if (stringConverter != null) {
+                                converter = Converter(
+                                    transform = { stringConverter.transform(this, (it as Char?)?.toString()) },
+                                    skipNulls = stringConverter.skipNulls,
+                                )
+                            }
+                        }
 
                         val convertedColumn = if (converter != null) {
                             val nullsAllowed = to.isMarkedNullable

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

@@ -564,29 +564,28 @@ internal fun <T> DataFrame<T>.parseImpl(options: ParserOptions?, columns: Column
         when {
             // when a frame column is requested to be parsed,
             // parse each value/frame column at any depth inside each DataFrame in the frame column
-            col.isFrameColumn() -> {
+            col.isFrameColumn() ->
                 col.map {
                     it.parseImpl(options) {
                         colsAtAnyDepth { !it.isColumnGroup() }
                     }
                 }
-            }
 
             // when a column group is requested to be parsed,
             // parse each column in the group
-            col.isColumnGroup() -> {
+            col.isColumnGroup() ->
                 col.parseImpl(options) { all() }
                     .asColumnGroup(col.name())
                     .asDataColumn()
-            }
+
+            // Base case, parse the column as String if it's a `Char?` column
+            col.isSubtypeOf<Char?>() ->
+                col.cast<Char?>().map { it?.toString() }.tryParseImpl(options)
 
             // Base case, parse the column if it's a `String?` column
-            col.isSubtypeOf<String?>() -> {
+            col.isSubtypeOf<String?>() ->
                 col.cast<String?>().tryParseImpl(options)
-            }
 
-            else -> {
-                col
-            }
+            else -> col
         }
     }

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

@@ -3,6 +3,7 @@ package org.jetbrains.kotlinx.dataframe.api
 import io.kotest.assertions.throwables.shouldNotThrow
 import io.kotest.assertions.throwables.shouldThrow
 import io.kotest.matchers.shouldBe
+import io.kotest.matchers.shouldNotBe
 import kotlinx.datetime.Clock
 import kotlinx.datetime.Instant
 import kotlinx.datetime.LocalTime
@@ -69,6 +70,20 @@ class ConvertTests {
     @Test
     fun `convert string to enum`() {
         columnOf("A", "B").convertTo<EnumClass>() shouldBe columnOf(EnumClass.A, EnumClass.B)
+
+        dataFrameOf(columnOf("A", "B") named "colA")
+            .convert("colA").to<EnumClass>()
+            .getColumn("colA") shouldBe columnOf(EnumClass.A, EnumClass.B).named("colA")
+    }
+
+    @Test
+    fun `convert char to enum`() {
+        // Char -> String -> Enum
+        columnOf('A', 'B').convertTo<EnumClass>() shouldBe columnOf(EnumClass.A, EnumClass.B)
+
+        dataFrameOf(columnOf('A', 'B') named "colA")
+            .convert("colA").to<EnumClass>()
+            .getColumn("colA") shouldBe columnOf(EnumClass.A, EnumClass.B).named("colA")
     }
 
     @JvmInline
@@ -199,6 +214,15 @@ class ConvertTests {
         val col = columnOf(65, 66)
         col.convertTo<Char>() shouldBe columnOf('A', 'B')
         col.convertTo<Char>().convertTo<Int>() shouldBe col
+
+        // this means
+        columnOf('1', '2').convertToInt() shouldNotBe columnOf(1, 2)
+        columnOf('1', '2').convertToInt() shouldBe columnOf(49, 50)
+
+        // but
+        columnOf('1', '2').convertToString().convertToInt() shouldBe columnOf(1, 2)
+        // or
+        columnOf('1', '2').parse() shouldBe columnOf(1, 2)
     }
 
     @Test

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

@@ -51,6 +51,38 @@ class ConvertToTests {
         df.convertTo<Schema> { parser { A(it.toInt()) } }
             .single()
             .a.value shouldBe 1
+
+        // shortcut for:
+        df.convertTo<Schema> { convert<String>().with { A(it.toInt()) } }
+            .single()
+            .a.value shouldBe 1
+    }
+
+    @Test
+    fun `convert from char with parser`() {
+        val df = dataFrameOf("a")('1')
+
+        shouldThrow<TypeConverterNotFoundException> {
+            df.convertTo<Schema>()
+        }
+
+        // Char -> String -> Target
+        df.convertTo<Schema> { parser { A(it.toInt()) } }
+            .single()
+            .a.value shouldBe 1
+
+        // shortcut for:
+        df.convertTo<Schema> { convert<String>().with { A(it.toInt()) } }
+            .single()
+            .a.value shouldBe 1
+
+        // Char -> Target
+        df.convertTo<Schema> {
+            parser<A> { error("should not be triggered if convert<Char>() is present") }
+            convert<String>().with<_, A> { error("should not be triggered if convert<Char>() is present") }
+
+            convert<Char>().with { A(it.digitToInt()) }
+        }.single().a.value shouldBe 1
     }
 
     @Test

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

@@ -32,6 +32,22 @@ import java.time.Duration as JavaDuration
 import java.time.Instant as JavaInstant
 
 class ParseTests {
+
+    @Test
+    fun `parse chars to string`() {
+        val char = columnOf('a', 'b', 'c')
+        char.parse() shouldBe columnOf("a", "b", "c")
+        char.tryParse() shouldBe columnOf("a", "b", "c")
+        char.parse().cast<String>().parse() shouldBe char
+    }
+
+    @Test
+    fun `parse chars to int`() {
+        val char = columnOf('1', '2', '3')
+        char.parse() shouldBe columnOf(1, 2, 3)
+        char.tryParse() shouldBe columnOf(1, 2, 3)
+    }
+
     @Test
     fun parseDate() {
         val currentLocale = Locale.getDefault()

core/src/test/kotlin/org/jetbrains/kotlinx/dataframe/io/ParserTests.kt

@@ -46,6 +46,12 @@ class ParserTests {
         DataFrame.parser.resetToDefault()
     }
 
+    @Test
+    fun `parse to Char`() {
+        val col by columnOf("a", "b")
+        col.parse().type() shouldBe typeOf<Char>()
+    }
+
     @Test(expected = IllegalStateException::class)
     fun `parse should throw`() {
         val col by columnOf("a", "bc")