Implement indices, index and rindex.

jaq-std/src/std.jq

@@ -117,6 +117,28 @@ def any: any(.[]; .);
 def in(xs)    : . as $x | xs | has     ($x);
 def inside(xs): . as $x | xs | contains($x);
 
+# Indexing
+def indices($i):
+  def enumerate:
+    . as $thing |
+    if type == "string"
+    then range(length) | [., $thing[.:.+1]]
+    else range(length) | [., $thing[.]]
+    end;
+
+  def windowed($size):
+    if $size <= 0 then empty
+    else . as $array | range(length - $size + 1) | $array[.:. + $size]
+    end;
+
+  if ($i | type) == "array" or (type == "string" and ($i | type) == "string")
+  then [[windowed($i | length)] | enumerate | select(.[1] == $i)[0]]
+  else [enumerate | select(.[1] == $i)[0]]
+  end;
+
+def index($i):  indices($i) | .[0];
+def rindex($i): indices($i) | .[-1:][0];
+
 # Walking
 def walk(f): def rec: (.[]? |= rec) | f; rec;
 

jaq-std/tests/std.rs

@@ -104,6 +104,27 @@ yields!(flatten_obj, "{a: 1} | flatten", json!([{"a": 1}]));
 // jq gives an error here
 yields!(flatten_num, "0 | flatten", [0]);
 
+#[test]
+fn indices() {
+    give(
+        json!("a,b, cd, efg, hijk"),
+        r#"indices(", ")"#,
+        json!([3, 7, 12]),
+    );
+    give(json!([0, 1, 2, 1, 3, 1, 4]), "indices(1)", json!([1, 3, 5]));
+    give(
+        json!([0, 1, 2, 3, 1, 4, 2, 5, 1, 2, 6, 7]),
+        "indices([1, 2])",
+        json!([1, 8]),
+    );
+    give(json!([]), "indices([])", json!([]));
+    give(json!([1, 2]), "indices([1, 2, 3])", json!([]));
+    give(json!(["a", "b", "c"]), r#"indices("b")"#, json!([1]));
+    give(json!([0, 0, 0]), "indices([0, 0])", json!([0, 1]));
+    // This is a discrepancy with jq: jq simply gives [0] and doesn't report the second match
+    give(json!("aaa"), r#"indices("aa")"#, json!([0, 1]));
+}
+
 #[test]
 fn inside() {
     give(