How do I round to the nearest 0.5?

Question

I have to display ratings and for that i need increments as follows:

If the number is 1.0 it should be equal to 1
If the number is 1.1 should be equal to 1
If the number is 1.2 should be equal to 1
If the number is 1.3 should be equal to 1.5
If the number is 1.4 should be equal to 1.5
If the number is 1.5 should be equal to 1.5
If the number is 1.6 should be equal to 1.5
If the number is 1.7 should be equal to 1.5
If the number is 1.8 should be equal to 2.0
If the number is 1.9 should be equal to 2.0
If the number is 2.0 should be equal to 2.0
If the number is 2.1 should be equal to 2.0
and so on...

Is there a simple way to compute the required values?

Answer 1

Multiply your rating by 2, then round using Math.Round(rating, MidpointRounding.AwayFromZero), then divide that value by 2.

Answer 2

Multiply by 2, round, then divide by 2

if you want nearest quarter, multiply by 4, divide by 4, etc

Answer 3

decimal d = // your number..

decimal t = d - Math.Floor(d);
if(t >= 0.3d && t <= 0.7d)
{
    return Math.Floor(d) + 0.5d;
}
else if(t>0.7d)
    return Math.Ceil(d);
return Math.Floor(d);

Answer 4

There are several options. If performance is a concern, test them to see which works fastest in a large loop.

double Adjust(double input)
{
    double whole = Math.Truncate(input);
    double remainder = input - whole;
    if (remainder < 0.3)
    {
        remainder = 0;
    }
    else if (remainder < 0.8)
    {
        remainder = 0.5;
    }
    else
    {
        remainder = 1;
    }
    return whole + remainder;
}

Answer 5

Sounds like you need to round to the nearest 0.5. I see no version of round in the C# API that does this (one version takes a number of decimal digits to round to, which isn't the same thing).

Assuming you only have to deal with integer numbers of tenths, it's sufficient to calculate round (num * 2) / 2. If you're using arbitrarily precise decimals, it gets trickier. Let's hope you don't.

Answer 6

I had difficulty with this problem as well. I code mainly in Actionscript 3.0 which is base coding for the Adobe Flash Platform, but there are simularities in the Languages:

The solution I came up with is the following:

//Code for Rounding to the nearest 0.05
var r:Number = Math.random() * 10;  // NUMBER - Input Your Number here
var n:int = r * 10;   // INTEGER - Shift Decimal 2 places to right
var f:int = Math.round(r * 10 - n) * 5;// INTEGER - Test 1 or 0 then convert to 5
var d:Number = (n + (f / 10)) / 10; //  NUMBER - Re-assemble the number

trace("ORG No: " + r);
trace("NEW No: " + d);

Thats pretty much it. Note the use of 'Numbers' and 'Integers' and the way they are processed.

Good Luck!