Add map() function

Proposed in jmespath/jmespath.site#15

Author: jamesls

jmespath/functions.py

@@ -251,6 +251,13 @@ def _func_floor(self, arg):
     def _func_join(self, separator, array):
         return separator.join(array)
 
+    @builtin_function({'types': ['expref']}, {'types': ['array']})
+    def _func_map(self, expref, arg):
+        result = []
+        for element in arg:
+            result.append(self.interpreter.visit(expref.expression, element))
+        return result
+
     @builtin_function({"types": ['array-number', 'array-string']})
     def _func_max(self, arg):
         if arg:

tests/compliance/functions.json

@@ -746,4 +746,61 @@
       ]
     }
   ]
-}]
+}, {
+  "given":
+  {
+    "people": [
+         {"a": 10, "b": 1, "c": "z"},
+         {"a": 10, "b": 2, "c": null},
+         {"a": 10, "b": 3},
+         {"a": 10, "b": 4, "c": "z"},
+         {"a": 10, "b": 5, "c": null},
+         {"a": 10, "b": 6},
+         {"a": 10, "b": 7, "c": "z"},
+         {"a": 10, "b": 8, "c": null},
+         {"a": 10, "b": 9}
+    ]
+  },
+  "cases": [
+    {
+      "expression": "map(&a, people)",
+      "result": [10, 10, 10, 10, 10, 10, 10, 10, 10]
+    },
+    {
+      "expression": "map(&c, people)",
+      "result": ["z", null, null, "z", null, null, "z", null, null]
+    },
+    {
+      "expression": "map(&a, badkey)",
+      "error": "invalid-type"
+    }
+  ]
+}, {
+  "given": {
+    "array": [
+      {
+          "foo": {"bar": "yes1"}
+      },
+      {
+          "foo": {"bar": "yes2"}
+      },
+      {
+          "foo1": {"bar": "no"}
+      }
+  ]},
+  "cases": [
+    {
+      "expression": "map(&foo.bar, array)",
+      "result": ["yes1", "yes2", null]
+    },
+    {
+      "expression": "map(&foo1.bar, array)",
+      "result": [null, null, "no"]
+    },
+    {
+      "expression": "map(&foo.bar.baz, array)",
+      "result": [null, null, null]
+    }
+  ]
+}
+]