From 16d0e528aa19ae2688460b1850adfd3737be4dcd Mon Sep 17 00:00:00 2001
From: pkoppstein <pkoppstein@gmail.com>
Date: Tue, 11 Aug 2015 02:50:48 -0400
Subject: [PATCH] walk/1

---
 builtin.c                        | 11 +++++++++++
 docs/content/3.manual/manual.yml | 27 +++++++++++++++++++++++++++
 2 files changed, 38 insertions(+)

diff --git a/builtin.c b/builtin.c
index 2fa498bb..990e24a9 100644
--- a/builtin.c
+++ b/builtin.c
@@ -1640,7 +1640,18 @@ static const char* const jq_builtins[] = {
   "      else .[2]"
   "      end"
   "  end;",
+
+  // # Apply f to composite entities recursively, and to atoms
+  "def walk(f):"
+  "  . as $in"
+  "  | if type == \"object\" then"
+  "      reduce keys[] as $key"
+  "        ( {}; . + { ($key):  ($in[$key] | walk(f)) } ) | f"
+  "  elif type == \"array\" then map( walk(f) ) | f"
+  "  else f"
+  "  end;",
 };
+
 #undef LIBM_DDD_NO
 #undef LIBM_DD_NO
 #undef LIBM_DDD
diff --git a/docs/content/3.manual/manual.yml b/docs/content/3.manual/manual.yml
index 0f1c2e92..89dcad2a 100644
--- a/docs/content/3.manual/manual.yml
+++ b/docs/content/3.manual/manual.yml
@@ -1522,6 +1522,33 @@ sections:
                 - 4
                 - 16
 
+      - title: "`walk(f)`"
+        body: |
+
+          The `walk(f)` function applies f recursively to every
+	  component of the input entity.  When an array is
+	  encountered, f is first applied to its elements and then to
+	  the array itself; when an object is encountered, f is first
+	  applied to all the values and then to the object.  In
+	  practice, f will usually test the type of its input, as
+	  illustrated in the following examples.  The first example
+	  highlights the usefulness of processing the elements of an
+	  array of arrays before processing the array itself.  The second
+	  example shows how all the keys of all the objects within the
+	  input can be considered for alteration.
+
+        examples:
+          - program: 'walk(if type == "array" then sort else . end)'
+            input: '[[4, 1, 7], [8, 5, 2], [3, 6, 9]]'
+            output:
+              - '[[1,4,7],[2,5,8],[3,6,9]]'
+
+          - program: 'walk( if type == "object" then with_entries( .key |= sub( "^_+"; "") ) else . end )
+            input: '[ { "_a": { "__b": 2 } } ]'
+            output:
+              - '[{"a":{"b":2}}]'
+
+
       - title: "`..`"
         body: |