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I need help converting a string that contains a number in scientific notation to a double.

Example strings: "1.8281e-009" "2.3562e-007" "0.911348"

I was thinking about just breaking the number into the number on the left and the exponent and than just do the math to generate the number; but is there a better/standard way to do this?

Bilal Shahid
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8 Answers8

17

PHP is typeless dynamically typed, meaning it has to parse values to determine their types (recent versions of PHP have type declarations).

In your case, you may simply perform a numerical operation to force PHP to consider the values as numbers (and it understands the scientific notation x.yE-z).

Try for instance

  foreach (array("1.8281e-009","2.3562e-007","0.911348") as $a)
  {
    echo "String $a: Number: " . ($a + 1) . "\n";
  }

just adding 1 (you could also subtract zero) will make the strings become numbers, with the right amount of decimals.

Result:

  String 1.8281e-009: Number: 1.0000000018281
  String 2.3562e-007: Number: 1.00000023562
  String 0.911348:    Number: 1.911348

You might also cast the result using (float)

  $real = (float) "3.141592e-007";
Déjà vu
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    It's not typeless. You can still distinguish between (for example) strings and ints with `is_string` and `is_int`. It's dynamically typed, with a lot of implicit conversions. Other than that, this is a good answer. – Matthew Flaschen Jan 02 '11 at 03:21
  • oh, didn't know php understands scientific notation. This is exactly what I needed. Thanks – Bilal Shahid Jan 02 '11 at 03:23
  • @Matthew I said *programming wise*. When programming, you do not have specifically to care about the types. Of course, internally PHP stores types. *Dynamically typed* is more appropriate - but I'm not sure a beginner will understand that definition better. – Déjà vu Jan 02 '11 at 03:23
  • you still sometimes need to distinguish when programming ordinary PHP code. For instance, a function might use `is_array` to test a parameter, and throw an exception if it's false. – Matthew Flaschen Jan 02 '11 at 03:26
  • @Matthew agreed, and I edited the answer. The *typeless* is by opposition to *C* for instance, where all objects have to be clearly and definitely associated to a type. – Déjà vu Jan 02 '11 at 03:30
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    -1, your solution loses precision. Casting to float is more accurate. – Ondergetekende Oct 03 '12 at 10:16
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    Would it still lose precision if you do "1.8281e-009" + 0? – Michael Butler Mar 29 '13 at 17:01
11
$f = (float) "1.8281e-009";
var_dump($f); // float(1.8281E-9)
Matthew
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8

Following line of code can help you to display bigint value,

$token=  sprintf("%.0f",$scienticNotationNum );

refer with this link.

ShivarajRH
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5
$float = sprintf('%f', $scientific_notation);
$integer = sprintf('%d', $scientific_notation);
if ($float == $integer) {
    // this is a whole number, so remove all decimals
    $output = $integer;
} else {
    // remove trailing zeroes from the decimal portion
    $output = rtrim($float,'0');
    $output = rtrim($output,'.');
}
Luca Borrione
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4

I found a post that used number_format to convert the value from a float scientific notation number to a non-scientific notation number:

Example from the post:

$big_integer = 1202400000; 
$formatted_int = number_format($big_integer, 0, '.', ''); 
echo $formatted_int; //outputs 1202400000 as expected
Dharman
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Jeff V
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4

Use number_format() and rtrim() functions together. Eg

//eg $sciNotation = 2.3649E-8
$number = number_format($sciNotation, 10); //Use $dec_point large enough
echo rtrim($number, '0'); //Remove trailing zeros

I created a function, with more functions (pun not intended)

function decimalNotation($num){
    $parts = explode('E', $num);
    if(count($parts) != 2){
        return $num;
    }
    $exp = abs(end($parts)) + 3;
    $decimal = number_format($num, $exp);
    $decimal = rtrim($decimal, '0');
    return rtrim($decimal, '.');
}
aphoe
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2
function decimal_notation($float) {
        $parts = explode('E', $float);

        if(count($parts) === 2){
            $exp = abs(end($parts)) + strlen($parts[0]);
            $decimal = number_format($float, $exp);
            return rtrim($decimal, '.0');
        }
        else{
            return $float;
        }
    }

work with 0.000077240388

falselight
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1

I tried the +1,-1,/1 solution but that was not sufficient without rounding the number afterwards using round($a,4) or similar

David Robertson
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