Review of VB.NET Data Storage Structures
Part five of an eight-part series of blogs

There are a bewildering array (excuse the pun) of data storage structures available to you in Visual Basic. Choose from arrays, ArrayLists, SortedLists, Dictionaries, HashTables, Lists and DataTables, among others. This blog gives an example of each type of structure, and benchmarks them to show which perform best and worst.

  1. VB.NET Data Storage Types Compared and Benchmarked
  2. VB.NET Benchmarking Test of speeds of data structures
  3. Arrays - Visual Basic data structures
  4. ArrayLists and SortedLists - Visual Basic data structures
  5. Dictionaries and HashTables - Visual Basic data structures (this blog)
  6. Lists - Visual Basic data structures
  7. Using data tables - Visual Basic data structures
  8. Benchmark Results and Recommendations

Posted by Andy Brown on 24 August 2011

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Dictionaries and HashTables

Dictionaries and hashtables are similar: they both store information in key/value pairs (exactly what we want to do for our example). 

Dictionary

Here is the code we use to test dictionary access:

Sub DictionaryTest()

Dim d As New Dictionary(Of String, Integer)

StartTimer()

'first test: writing 10 ^ n values, increasing size of the array by 1 each time

Dim i As Integer

For i = 0 To (10 ^ RunSize) - 1

d.Add(TestCode(i), i)

Next

'work out how long this took

WriteTime = ElapsedTime

'store ten values for subsequent tests

StoreTenValues()

'sort the dictionary (get list of keys first)

Dim keys As List(Of String) = d.Keys.ToList

keys.Sort()

SortTime = ElapsedTime

'third test: find 10 "random" values by number

Dim s As String

For i = (10 ^ RunSize) - 1 To 0 Step -(10 ^ (RunSize - 1))

s = d.Keys(i)

Next

'report how long this took

Read1Time = ElapsedTime

'fourth test: find 10 "random" values by name

For i = 0 To 9

s = d.Item(TextValues(i))

Next

Read2Time = ElapsedTime

'write out results of test

AddRow("Dictionary")

End Sub

HashTable

The code I used to test hashtable access is as follows:

Sub TestHashTable()

Dim ht As New Hashtable

StartTimer()

'first test: writing 10 ^ n values, increasing size of the array by 1 each time

Dim i As Integer

For i = 0 To (10 ^ RunSize) - 1

ht(i) = TestCode(i)

Next

'work out how long this took

WriteTime = ElapsedTime

'store ten values for subsequent tests

StoreTenValues()

'hash tables don't support native sorting

SortTime = 0

'third test: find 10 "random" values by number

Dim s As String

For i = (10 ^ RunSize) - 1 To 0 Step -(10 ^ (RunSize - 1))

s = ht.Keys(i)

Next

'report how long this took

Read1Time = ElapsedTime

'fourth test: find 10 "random" values by name

For i = 0 To 9

s = ht(TextValues(i))

Next

Read2Time = ElapsedTime

'write out results of test

AddRow("Hash Table")

End Sub

The results of running these tests are shown at the end of this blog.

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