Create update.md

Author: omkarhole

content/dart/concepts/map/terms/update/update.md

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+---
+Title: '.update()'
+Description: 'Updates the value for a specific key in a Map using a provided function.'
+Subjects:
+  - 'Computer Science'
+  - 'Code Foundations'
+Tags:
+  - 'Dart'
+  - 'Methods'
+  - 'Map'
+CatalogContent:
+  - 'learn-dart'
+  - 'paths/computer-science'
+---
+
+In Dart, the **`.update()`** method is used to update the value for a specific key in a `Map`. It takes a key and a function that computes the new value based on the existing value. If the key does not exist, an optional `ifAbsent` function can be provided to add a new key-value pair.
+
+## Syntax
+
+```pseudo
+mapVariable.update(key, (value) => newValue)
+```
+
+- `mapVariable`: The `Map` to be updated.
+- `key`: The key whose value needs to be updated.
+- `value`: The current value associated with the key.
+- `newValue`: The new value to replace the existing value.
+
+An optional `ifAbsent` parameter can be used to add a key if it does not exist:
+
+```pseudo
+mapVariable.update(key, (value) => newValue, ifAbsent: () => defaultValue)
+```
+
+- `ifAbsent`: A function that returns a default value if the key is not found.
+
+## Example 1
+
+In the following example, the `.update()` method is used to update the value for an existing key in a `Map`:
+
+```dart
+void main() {
+  Map<String, int> fruits = {'Apple': 5, 'Banana': 3};
+
+  // Update the value for 'Apple'
+  fruits.update('Apple', (value) => value + 2);
+
+  print(fruits);
+}
+```
+
+Here is the output for the above example:
+
+```shell
+{Apple: 7, Banana: 3}
+```
+
+## Example 2
+
+The `.update()` method can use the `ifAbsent` parameter to add a key if it does not exist:
+
+```dart
+void main() {
+  Map<String, int> fruits = {'Apple': 5};
+
+  // 'Orange' does not exist, so ifAbsent adds it
+  fruits.update('Orange', (value) => value, ifAbsent: () => 10);
+
+  print(fruits);
+}
+```
+
+Here is the output for the above example:
+
+```shell
+{Apple: 5, Orange: 10}
+```
+
+## Example 3
+
+The `.update()` method can also work with different [data types](https://www.codecademy.com/resources/docs/dart/data-types) for keys and values:
+
+```dart
+void main() {
+  Map<int, String> students = {1: 'Alice', 2: 'Bob'};
+
+  // Update the value for key 1
+  students.update(1, (value) => '$value Smith');
+
+  print(students);
+}
+```
+
+Here is the output for the above example:
+
+```shell
+{1: Alice Smith, 2: Bob}
+```