diff --git a/src/jsonData.js b/src/jsonData.js
index fb95332..96cc575 100644
--- a/src/jsonData.js
+++ b/src/jsonData.js
@@ -486,6 +486,8 @@ export function expand (data, callback, expanded) {
  * @private
  */
 function expandRecursive (data, path, callback, expanded) {
+  // TODO: use the function transform here?
+
   switch (data.type) {
     case 'Array': {
       let updatedData = callback(path)
@@ -543,24 +545,74 @@ export function addErrors (data, errors) {
 }
 
 /**
- * Remove errors which where added using addErrors
+ * Merge one or multiple errors (for example JSON schema errors)
+ * into the data
  *
  * @param {JSONData} data
- * @param {Array.<JSONSchemaError>} errors
+ * @param {string} search
  */
-export function removeErrors (data, errors) {
+export function setSearch (data, search) {
   let updatedData = data
 
-  errors.forEach(error => {
-    const dataPath = toDataPath(data, parseJSONPointer(error.dataPath))
-    updatedData = deleteIn(updatedData, dataPath.concat('error'))
-  })
+  // TODO: traverse over the data, add a field search: 'field'|'value' to all matching fields/values
 
   return updatedData
 }
 
-// TODO: implement a function removeAllErrors (data)
+/**
+ *
+ * @param {JSONData} data
+ * @param {function(value: JSONData, path: Path, root: JSONData)} callback
+ * @return {JSONData} Returns the transformed data
+ */
+export function transform (data, callback) {
+  return recurseTransform (data, [], data, callback)
+}
 
+/**
+ * Recursively transform JSONData
+ * @param {JSONData} value
+ * @param {Path} path
+ * @param {JSONData | null} root    The root object, object at path=[]
+ * @param {function(value: JSONData, path: Path, root: JSONData)} callback
+ * @return {JSONData} Returns the transformed data
+ */
+function recurseTransform (value, path, root, callback) {
+  let updatedValue = callback(value, path, root)
+
+  switch (value.type) {
+    case 'Array': {
+      let updatedItems = updatedValue.items
+
+      updatedValue.items.forEach((item, index) => {
+        updatedItems = setIn(updatedItems, [index],
+            recurseTransform(item, path.concat(String(index)), root, callback))
+      })
+
+      updatedValue = setIn(updatedValue, ['items'], updatedItems)
+
+      break
+    }
+
+    case 'Object': {
+      let updatedProps = updatedValue.props
+
+      updatedValue.props.forEach((prop, index) => {
+        updatedProps = setIn(updatedProps, [index, 'value'],
+            recurseTransform(prop.value, path.concat(prop.name), root, callback))
+      })
+
+      updatedValue = setIn(updatedValue, ['props'], updatedProps)
+
+      break
+    }
+
+    default: // type 'string' or 'value'
+      // don't do anything: a value can't be expanded, only arrays and objects can
+  }
+
+  return updatedValue
+}
 
 /**
  * Test whether a path exists in the json data
diff --git a/test/jsonData.test.js b/test/jsonData.test.js
index 4536aca..c85694b 100644
--- a/test/jsonData.test.js
+++ b/test/jsonData.test.js
@@ -1,8 +1,8 @@
 import test from 'ava';
 import {
-    jsonToData, dataToJson, patchData, pathExists,
+    jsonToData, dataToJson, patchData, pathExists, transform,
     parseJSONPointer, compileJSONPointer,
-    expand, addErrors, removeErrors
+    expand, addErrors
 } from '../src/jsonData'
 
 
@@ -736,7 +736,77 @@ test('jsonpatch test (fail: value not equal)', t => {
 test('add and remove errors', t => {
   const dataWithErrors = addErrors(JSON_DATA_EXAMPLE, JSON_SCHEMA_ERRORS)
   t.deepEqual(dataWithErrors, JSON_DATA_EXAMPLE_ERRORS)
-
-  const dataWithoutErrors = removeErrors(dataWithErrors, JSON_SCHEMA_ERRORS)
-  t.deepEqual(dataWithoutErrors, JSON_DATA_EXAMPLE)
+})
+
+test('transform', t => {
+  // {obj: {a: 2}, arr: [3]}
+  const data = {
+    type: 'Object',
+    props: [
+      {
+        name: 'obj',
+        value: {
+          type: 'Object',
+          props: [
+            {
+              name: 'a',
+              value: {
+                type: 'value',
+                value: 2
+              }
+            }
+          ]
+        }
+      },
+      {
+        name: 'arr',
+        value: {
+          type: 'Array',
+          items: [
+            {
+              type: 'value',
+              value: 3
+            }
+          ]
+        }
+      }
+    ]
+  }
+
+
+  let log = []
+  const transformed = transform(data, function (value, path, root) {
+    t.truthy(root === data)
+
+    log.push([value, path, root])
+
+    if (path.length === 2 && path[0] === 'obj' && path[1] === 'a') {
+      // change the value
+      return { type: 'value', value: 42 }
+    }
+
+    // leave the value unchanged
+    return value
+  })
+
+  // console.log('transformed', JSON.stringify(transformed, null, 2))
+
+  const EXPECTED_LOG = [
+    [data, [], data],
+    [data.props[0].value, ['obj'], data],
+    [data.props[0].value.props[0].value, ['obj', 'a'], data],
+    [data.props[1].value, ['arr'], data],
+    [data.props[1].value.items[0], ['arr', '0'], data],
+  ]
+
+  // log.forEach((row, index) => {
+  //   t.deepEqual(log[index], EXPECTED_LOG[index], 'should have equal log at index ' + index )
+  // })
+  t.deepEqual(log, EXPECTED_LOG)
+  t.truthy(transformed !== data)
+  t.truthy(transformed.props[0].value !== data.props[0].value)
+  t.truthy(transformed.props[0].value.props[0].value !== data.props[0].value.props[0].value)
+  t.truthy(data.props[1].value === data.props[1].value)
+  t.truthy(data.props[1].value.items[0] === data.props[1].value.items[0])
+
 })