Repeatedly checking entire scripting dictionary via loop bad practice? VB6

Question

I have a loop that checks for values and adds them to a dictionary if they do not exist. This check happens inside of a loop so it happens repeatedly. As the dictionary grows I imagine there is an inner loop going on with each check that is becoming costly. In an effort to speed up my entire routine I am wondering if this might be something I should optimize? If so, how?

  keycnt = 1
  For x = 1 to 500000
  STRVAL = returnarray(8, x)
            If Not STRDIC.Exists(STRVAL) Then
               STRDIC.Add STRVAL, keycnt
               keycnt = keycnt + 1
            End If
  next x

Where is STRVAL coming from? Without knowing that it's difficult to tell what you're asking here? In any case, the advantage of using a dictionary is that key lookups are very fast - typically lookup is via hashed keys and not just a simple loop. — Tim Williams
– Tim Williams, Commented Jun 10, 2016 at 17:26
It's just some value I set based on a recordset I am pulling using ADO. As I loop through the recordset I assign the value. I removed all of that to simplify my question because I don't really want anyone focusing on that. — Johnson Jason
– Johnson Jason, Commented Jun 10, 2016 at 17:33
your answer TIM is helping. That's what I am asking. Is it okay to hit the dictionary lookup repeatedly or is there a better method. — Johnson Jason
– Johnson Jason, Commented Jun 10, 2016 at 17:35
A better way is to add it, it will error if it already exists. Test for the error if you care. This way you only look up the dictionary once - when it is added. Your code searches twice - once to see if it exists and then when you add it. — user6017774
– user6017774, Commented Jun 11, 2016 at 22:07

Mathieu Guindon · Accepted Answer · 2016-06-10 17:40:00Z

4

If your dictionary is a Scripting.Dictionary and not some [poorly implemented] custom-made data structure class, then a key lookup should be O(1) complexity, not O(n) as you seem to imply; the growing number of keys has no impact on performance.

Key lookup in a hash table or dictionary is basically free, the only thing to fix in that code is the indentation.

edited Jun 10, 2016 at 17:40

answered Jun 10, 2016 at 17:36

Mathieu Guindon

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1 Comment

Johnson Jason Over a year ago

yes its a Scripting.Dictionary. Thank you Mat's Mug. I wasn't sure how the lookup in the dictionary was happening and I was afraid that nesting it in a giant loop was a mistake.

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