Adds #2176 slice() (#2238)

Adds a slice() function with documentation to the query language.

docs/docs/reference/functions.md

@@ -519,6 +519,18 @@ flat(list(1, list(21, 22), list(list (311, 312, 313))), 4) => list(1, 21, 22, 31
 flat(rows.file.outlinks)) => All the file outlinks at first level in output
 ```
 
+### `slice(array, [start, [end]])`
+
+Returns a shallow copy of a portion of an array into a new array object selected from `start`
+to `end` (`end` not included) where `start` and `end` represents the index of items in that array.
+
+```js
+slice([1, 2, 3, 4, 5], 3) = [4, 5] => All items from given position, 0 as first
+slice(["ant", "bison", "camel", "duck", "elephant"], 0, 2) = ["ant", "bison"] => First two items 
+slice([1, 2, 3, 4, 5], -2) = [4, 5] => counts from the end, last two items
+slice(someArray) => a copy of someArray
+```
+
 ---
 
 ## String Operations

src/expression/functions.ts

@@ -831,6 +831,20 @@ export namespace DefaultFunctions {
         })
         .add1("null", () => null)
         .build();
+
+    // Slices the array into a new array
+    export const slice = new FunctionBuilder("slice")
+        .add1("array", a => {
+            return a.slice();
+        })
+        .add2("array", "number", (a, start) => {
+            return a.slice(start);
+        })
+        .add3("array", "number", "number", (a, start, end) => {
+            return a.slice(start, end);
+        })
+        .add1("null", () => null)
+        .build();
 }
 
 /** Default function implementations for the expression evaluator. */
@@ -889,6 +903,7 @@ export const DEFAULT_FUNCTIONS: Record<string, FunctionImpl> = {
     reverse: DefaultFunctions.reverse,
     sort: DefaultFunctions.sort,
     flat: DefaultFunctions.flat,
+    slice: DefaultFunctions.slice,
 
     // Aggregation operations like reduce.
     reduce: DefaultFunctions.reduce,

src/test/function/functions.test.ts

@@ -72,6 +72,25 @@ test("Evaluate flat()", () => {
     expect(parseEval("flat(list(1, list(2, list(3, list(4, list(5))))), 10)")).toEqual(parseEval("list(1,2,3,4,5)")); // flat(..., 10)
 });
 
+// <-- slice() -->
+
+test("Evaluate slice()", () => {
+    expect(parseEval("slice(list(1, 2, 3, 4, 5), 3)")).toEqual(parseEval("list(4, 5)")); // slice(..., 3)
+    expect(parseEval("slice(list(1, 2, 3, 4, 5), 0, 2)")).toEqual(parseEval("list(1, 2)")); // slice(..., 0, 2)
+    expect(parseEval("slice(list(1, 2, 3, 4, 5), -2)")).toEqual(parseEval("list(4, 5)")); // slice(..., -2)
+    expect(parseEval("slice(list(1, 2, 3, 4, 5), -1, 1)")).toEqual(parseEval("list()")); // slice(..., -1, 1)
+    expect(parseEval("slice(list(1, 2, 3, 4, 5))")).toEqual(parseEval("list(1, 2, 3, 4, 5)")); // slice(...)
+    expect(parseEval('slice(list(date("2021-01-01"), date("2022-02-02"), date("2023-03-03")), -2)')).toEqual([
+        DateTime.fromObject({ year: 2022, month: 2, day: 2 }),
+        DateTime.fromObject({ year: 2023, month: 3, day: 3 }),
+    ]); // slice(date list, -2)
+    expect(parseEval('slice(["ant", "bison", "camel", "duck", "elephant"], -3)')).toEqual([
+        "camel",
+        "duck",
+        "elephant",
+    ]); // slice(string list, -3)
+});
+
 // <-- sort() -->
 
 describe("sort()", () => {