php - Rounding to nearest fraction (half, quarter, etc.)

Question

So, I need to create the following functions but my head can't think of any possibility in PHP without complicated math.

• Round always up to the nearest decimal (1.81 = 1.90, 1.89 = 1.90, 1.85 = 1.90)
• Round always down to the nearest decimal (1.81 = 1.80, 1.89 = 1.80, 1.85 = 1.80)
• Round always up to the nearest x.25 / x.50 / x.75 / x.00 (1.81 = 2, 1.32 = 1.50)
• Round always down to the nearest x.25 / x.50 / x.75 / x.00 (1.81 = 1.75, 1.32 = 1.25)
• Round always up to the nearest x.50 / 1 (1.23 = 1.50, 1.83 = 2)
• Round always down to the nearest x.50 / 1 (1.23 = 1, 1.83 = 1.50)

I have searched on Google for 2 hours now and the only things that came up were Excel forums. Is it possible with some simple lines of PHP?

Answer 1

Since you're looking for fourths (.00, .25, .50, .75), multiply your number by 4, round to nearest whole number as desired (floor if down, ceil if up), then divide by 4.

1.32, down to nearest fourth:

1.32 * 4 = 5.28
floor(5.28) = 5.00
5.00 / 4 = 1.25

Same principle applies for any other fractions, such as thirds or eighths (.0, .125, .25, .375, .5, .625, .75, .875). For example:

1.77, up to nearest eighth:

1.77 * 8 = 14.16
ceil(14.16) = 15.00
15.00 / 8 = 1.875

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Just for fun, you could write a function like this:

function floorToFraction($number, $denominator = 1)
{
    $x = $number * $denominator;
    $x = floor($x);
    $x = $x / $denominator;
    return $x;
}

echo floorToFraction(1.82);      // 1
echo floorToFraction(1.82, 2);   // 1.5
echo floorToFraction(1.82, 3);   // 1.6666666666667
echo floorToFraction(1.82, 4);   // 1.75
echo floorToFraction(1.82, 9);   // 1.7777777777778
echo floorToFraction(1.82, 25);  // 1.8