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How to use removeWhere() in Dart

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Overview

We can use the removeWhere() method to remove all the entries that satisfy the provided test condition.

Syntax

void removeWhere( bool test(K key,V value) )

Parameters

This method takes a test function that can take two arguments, key and value. It returns a Boolean value. This method is invoked for each entry of the SplayTreeMap.

The removeWhere method will iterate the SplayTreeMap and invoke the test function for each entry. If the test function returns true, then the current entry will be removed from the map.

Return value

This method doesn’t return any value.

Example

The code below demonstrates the use of the removeWhere() method to remove all entries of SplayTreeSet that match a provided test condition:

import 'dart:collection';
void main() {
  //create a new SplayTreeMap which can have int key and string values
  SplayTreeMap map = new SplayTreeMap<int, String>((keya,keyb) =>  keyb.compareTo(keya));

  // add five entries to the map
  map[5] = "Five";
  map[4] = "Four";
  map[3] = "Three";
  map[2] = "Two";
  map[1] = "One";

  print('The map is $map');

  // Remove the entry with odd keys
  map.removeWhere((key, value){
    return key % 2 != 0;
  });
  
  print('The map is $map');

}
Using removeWhere

Explanation

  • Line 1: We import the collection library.

  • Line 4: We create a new SplayTreeMap object with the name map. We pass a compare function as an argument. This function is used to maintain the order of the map entries. In our case, the compare function orders the elements in descending order.

  • Lines 7 to 11: We add five new entries to the map. Now, the map is {5: Five, 4: Four, 3: Three, 2: Two, 1: One}.

  • Line 16: We use the removeWhere() method with a test function as an argument. The test function returns true if the key is an odd value. In our case, the keys 1, 3, and 5 are the values, so these entries are removed from the map. After removing the odd value entries, the map will be {4: Four, 2: Two}.

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splaytreemap
removewhere
dart
communitycreator
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