# Array.Sort Method (Array, Array, Int32, Int32)

**.NET Framework 4.5**

Sorts a range of elements in a pair of one-dimensional Array objects (one contains the keys and the other contains the corresponding items) based on the keys in the first Array using the IComparable implementation of each key.

**Namespace:**System

**Assembly:**mscorlib (in mscorlib.dll)

#### Parameters

- keys
- Type: System.Array
The one-dimensional Array that contains the keys to sort.

- items
- Type: System.Array
The one-dimensional Array that contains the items that correspond to each of the keys in the keys Array.

-or-

a null reference (Nothing in Visual Basic) to sort only the keys Array.

- index
- Type: System.Int32
The starting index of the range to sort.

- length
- Type: System.Int32
The number of elements in the range to sort.

Exception | Condition |
---|---|

ArgumentNullException | keys is a null reference (Nothing in Visual Basic). |

RankException | The keys Array is multidimensional. -or- The items Array is multidimensional. |

ArgumentOutOfRangeException | index is less than the lower bound of keys. -or- length is less than zero. |

ArgumentException | items is not a null reference (Nothing in Visual Basic), and the length of keys is greater than the length of items. -or- index and length do not specify a valid range in the keys Array. -or- items is not a null reference (Nothing in Visual Basic), and index and length do not specify a valid range in the items Array. |

InvalidOperationException | One or more elements in the keys Array do not implement the IComparable interface. |

Each key in the keys Array has a corresponding item in the items Array. When a key is repositioned during the sorting, the corresponding item in the items Array is similarly repositioned. Therefore, the items Array is sorted according to the arrangement of the corresponding keys in the keys Array.

Each key within the specified range of elements in the keys Array must implement the IComparable interface to be capable of comparisons with every other key.

You can sort if there are more items than keys, but the items that have no corresponding keys will not be sorted. You cannot sort if there are more keys than items; doing this throws an ArgumentException.

If the sort is not successfully completed, the results are undefined.

This method uses the introspective sort (introsort) algorithm as follows:

If the partition size is fewer than 16 elements, it uses an insertion sort algorithm.

If the number of partitions exceeds 2 * LogN, where N is the range of the input array, it uses a Heapsort algorithm.

Otherwise, it uses a Quicksort algorithm.

This implementation performs an unstable sort; that is, if two elements are equal, their order might not be preserved. In contrast, a stable sort preserves the order of elements that are equal.

For arrays that are sorted by using the Heapsort and Quicksort algorithms, in the worst case, this method is an O(n log n) operation, where n is length.

The following code example shows how to sort two associated arrays where the first array contains the keys and the second array contains the values. Sorts are done using the default comparer and a custom comparer that reverses the sort order. Note that the result might vary depending on the current CultureInfo.