ColumnarData returns nullable column

CHANGELOG.md

@@ -29,6 +29,7 @@
 - Separated benchmarks and examples
 - Rewritten EJML module without ejml-simple
 - Stability of kmath-ast and kmath-kotilngrad promoted to EXPERIMENTAL.
+- ColumnarData returns nullable column
 
 ### Deprecated
 

kmath-core/src/commonMain/kotlin/space/kscience/kmath/data/ColumnarData.kt

@@ -19,7 +19,7 @@ import space.kscience.kmath.structures.Buffer
 public interface ColumnarData<out T> {
     public val size: Int
 
-    public operator fun get(symbol: Symbol): Buffer<T>
+    public operator fun get(symbol: Symbol): Buffer<T>?
 }
 
 /**

kmath-core/src/commonMain/kotlin/space/kscience/kmath/data/XYColumnarData.kt

@@ -27,10 +27,10 @@ public interface XYColumnarData<T, out X : T, out Y : T> : ColumnarData<T> {
      */
     public val y: Buffer<Y>
 
-    override fun get(symbol: Symbol): Buffer<T> = when (symbol) {
+    override fun get(symbol: Symbol): Buffer<T>? = when (symbol) {
         Symbol.x -> x
         Symbol.y -> y
-        else -> error("A column for symbol $symbol not found")
+        else -> null
     }
 }
 

kmath-core/src/commonMain/kotlin/space/kscience/kmath/data/XYZColumnarData.kt

@@ -17,10 +17,10 @@ import space.kscience.kmath.structures.Buffer
 public interface XYZColumnarData<T, out X : T, out Y : T, out Z : T> : XYColumnarData<T, X, Y> {
     public val z: Buffer<Z>
 
-    override fun get(symbol: Symbol): Buffer<T> = when (symbol) {
+    override fun get(symbol: Symbol): Buffer<T>? = when (symbol) {
         Symbol.x -> x
         Symbol.y -> y
         Symbol.z -> z
-        else -> error("A column for symbol $symbol not found")
+        else -> null
     }
 }