Round numbers to the nearest 0.5

[Mighty]

Hi Folks,

I need to be able to round a number to the nearest 0.5.

i.e. 21.3 rounds to 21.5
21.25 rounds to 21

Any suggestions on how to do this.

Just wondering if something like

Round(Round(2*myVal, 0)/2, 1)

would work consistently or if there is a better method

Nick

Mighty

 

[Mighty]

Actually,

that fornula won't work for 21.25 as it will round it to 21.5 which is not correct.

Any other suggestions.

Mighty

 

[gmmastros]

Try...

cInt(myVal * 2) / 2

For more information about rounding...

http://support.microsoft.com/default.aspx/kb/196652

-George

Strong and bitter words indicate a weak cause. - Fortune cookie wisdom

 

[Abraxus]

Since this is custom rounding, based on your own rules, I would write a quick function that ensures the right rounding:

Function myRounded(myVal)
   myVal = FormatNumber(myVal,2)
   myVal = Split(myVal,".")
   ' myVal(0) is the whole number before the decimal
   ' myVal(1) is the decimal value, two places
   myDec = cint(myVal(1))
   if myDec>25 and myDec<76 then
      myRounded = cDbl(myVal(0)+.5)
   else
      if myDec>75 then
         myRounded = cInt(myVal(0)+1)
      else
         myRounded = cInt(myVal(0))
      end if
   end if
End Function

Perhaps there's an easier way to do it, but that's how I would tackle a problem like this. I tested this function on my machine with a couple examples to ensure it follows your rules. It bascially looks at the decimal of the passed value as a two-digit number, then if it's between 26 and 75 it returns the original number with a .5, greater than 75 returns the original number +1, if it's 25 or less it will return the original number.

Eric

 

[Tarwn]

Wow, deja-vu. I swear someone asked this question in the past few years...good luck trying to find it though

I believe the double rounding will work consistently. Of course since I skipped over part of your question and already had a solution before I re-read your question and realized we worked it out similarly.

My multi-use function:

Function NearestRound(OrigNumber,nearDec)
   Dim factor: factor = 1/nearDec
   Dim baseNum, dec
   baseNum = Fix(OrigNumber)
   dec = Round((OrigNumber - baseNum)*factor,0)
   NearestRound = baseNum + dec/factor
End Function

Or a shorter version:
Function NearestRound(OrigNumber,nearDec)
   NearestRound = Fix(OrigNumber) + Round((OrigNumber - Fix(OrigNumber))/nearDec,0) * nearDec
End Function

OrigNumber is the number you wish to round, nearDec is the nearest decimal you wish to round to. So in this instance you would do something like:
Response.Write NearestRound(yourNumVar,.5)


I think the biggest difference between our methods is that rather than use a double round I ended up using the Fix function. Round() is not always as consistent as you would think it would be. I believe it uses Bankers rounding, but I could be mis-remembering. So I used a Fix() statement to take the non-decimal portion out of the equation.

Looking at it more, I'm almost thinking that you could use a single round and consistently get the correct number:

Function NearestRound(OrigNumber,nearDec)
   NearestRound = Round(OrigNumber/nearDec,0) * nearDec
End Function

The only concern I would have is large floats that might cause vbscript to add/subtract .000000001 to them when you do the end multiplication.

-T

 

[Mighty]

Thanks for all the suggestions guys

Mighty