PHP dropping decimals without rounding up

Question

I want to drop off decimals without rounding up. For example if I have 1.505, I want to drop last decimal and value should be 1.50. Is there such a function in PHP?

Answer 1

To do this accurately for both +ve and -ve numbers you need use:
- the php floor() function for +ve numbers
- the php ceil() function for -ve numbers

function truncate_float($number, $decimals) {
    $power = pow(10, $decimals); 
    if($number > 0){
        return floor($number * $power) / $power; 
    } else {
        return ceil($number * $power) / $power; 
    }
}

the reason for this is that floor() always rounds the number down, not towards zero.
ie floor() effectively rounds -ve numbers towards a larger absolute value
eg floor(1.5) = 1 while floor(-1.5) = -2

Therefore, for the multiply by power, remove decimals, divide by power truncate method :
- floor() only works for positive numbers
- ceil() only works for negative numbers

To test this, copy the following code into the editor of http://phpfiddle.org/lite (or similar):

<div>Php Truncate Function</div>
<br>
<?php
    function truncate_float($number, $places) {
        $power = pow(10, $places); 
        if($number > 0){
            return floor($number * $power) / $power; 
        } else {
            return ceil($number * $power) / $power; 
        }
    }

    // demo
    $lat = 52.4884;
    $lng = -1.88651;
    $lat_tr = truncate_float($lat, 3);
    $lng_tr = truncate_float($lng, 3);
    echo 'lat = ' . $lat . '<br>';
    echo 'lat truncated = ' . $lat_tr . '<br>';
    echo 'lat = ' . $lng . '<br>';
    echo 'lat truncated = ' . $lng_tr . '<br><br>';

    // demo of floor() on negatives
    echo 'floor (1.5) = ' . floor(1.5) . '<br>';
    echo 'floor (-1.5) = ' . floor(-1.5) . '<br>';
?>

Answer 2

The answers of RenaPot, IsisCode, goredwards are not correct.

Because of how float works in computers (in general), float is not accurate.

To replicate the issue:

floor(19.99 * 100);  // Outputs 1998 instead of 1999
floor( 5.10 * 100);  // Outputs  509 instead of  510

Within PHP internally, 19.99 * 100 results in something like 1998.999999999999999, which when we do floor of that, we get 1998.

Solution:

Solution 1: Use bcmath library (Suggested by @SamyMassoud) if you have it installed (some shared hosting servers may not have it installed by default). Like so:

//floor(19.99 * 100);// Original
floor(bcmul(19.99, 100));// Outputs 1999

Solution 2: String manipulation (my recommendation):

// Works with positive and negative numbers, and integers and floats and strings
function withoutRounding($number, $total_decimals) {
    $number = (string)$number;
    if($number === '') {
        $number = '0';
    }
    if(strpos($number, '.') === false) {
        $number .= '.';
    }
    $number_arr = explode('.', $number);

    $decimals = substr($number_arr[1], 0, $total_decimals);
    if($decimals === false) {
        $decimals = '0';
    }

    $return = '';
    if($total_decimals == 0) {
        $return = $number_arr[0];
    } else {
        if(strlen($decimals) < $total_decimals) {
            $decimals = str_pad($decimals, $total_decimals, '0', STR_PAD_RIGHT);
        }
        $return = $number_arr[0] . '.' . $decimals;
    }
    return $return;
}

// How to use:
withoutRounding(19.99, 2);// Return "19.99"
withoutRounding(1.505, 2);// Return "1.50"
withoutRounding(5.1, 2);// Return "5.10"

Answer 3

Maybe it's too late, but here's a good approach:

    $getTruncatedValue = function( $value, $precision )
    {
        //Casts provided value
        $value = ( string )$value;

        //Gets pattern matches
        preg_match( "/(-+)?\d+(\.\d{1,".$precision."})?/" , $value, $matches );

        //Returns the full pattern match
        return $matches[0];            
    };

    var_dump
    (
        $getTruncatedValue(1.123,1),   //string(3) "1.1"
        $getTruncatedValue(1.345,2),   //string(4) "1.34"
        $getTruncatedValue(1.678,3),   //string(5) "1.678"
        $getTruncatedValue(1.90123,4)  //string(6) "1.9012"  
    );

• The only pitfall in this approach may be the need to use a Regular Expression (which sometimes could bring a performance penalty).

Note: It's quite hard to find a native approach to truncate decimals, and I think it's not possible to perform that using sprintf and other string-related functions.

Answer 4

To avoid using ceil, floor and round, just treat it as a string and cut it if necessary. This avoids all the rounding issues.

The code below looks for the first 2 numbers after the dot and singles them out. Then it looks for any numbers that trail that. It then replaces the entire thing with only the 2 numbers it found. If number doesn't match the replace rule, nothing changes.

You could stick this in a function call and pass the function the number and the quantity of numbers you want to keep after the decimal place.

    // Shorten number to 2 decimal places without rounding
    $num = 2213.145;
    $num = floatval(preg_replace("/\.([0-9]{2})[0-9]{0,99}/",".$1",$num));

Answer 5

Its easy and work better.

$value = 12.9987876;
$value_exp = explode(".", $value);
$value_new = floatval($value_exp[0].'.'.substr($value_exp[1],0,4));

echo $value_new; // output will 12.9987

Answer 6

just do (int) $number; to get integer