how to use operators in an array for operations

Question

I realize that arrays were not built this way in PHP. however I am experimenting with genetic algorithms for the first time, and as PHP is the language most familiar to me, I am writting it in PHP, later I will change it to Python. Anyway, i have two input arrays, one of which being:

$geneValues = array(
    '0000' => 0,
    '0001' => 1,
    '0010' => 2,
    '0011' => 3,
    '0100' => 4,
    '0101' => 5,
    '0110' => 6,
    '0111' => 7,
    '1000' => 8,
    '1001' => 9,
    '1010' => '+',
    '1011' => '-',
    '1100' => '*',
    '1101' => '/');

each key is a "gene" that stores a value. I am attempting to do this completely hands off other than the initial array setting, i have a function that creates The initial population by randomly combining the above array genes into a multidimensional array which groups the genes into, you guessed it, chromosomes. so i could have a chromosome that looks like: 011010100111 meaning => 6 + 7 this all works great. However I am at the point where I need to actually "compute" the chromosome, however as the addition operator has to be in quotes in the array, it makes a literal + and not the operator. My question is, is there any way that I can get the operators in my array to be actual operators, I know of know function that will do this, and the only other option i can come up with would be to hard code the gene to the operator when i do the computations, which is what im trying to avoid.

I will post the whole code if needed, it's nothing sensitive, just trying to ease my way into neural networks and figured i would start with implementing genetic algorithms. Any one have a solution?

Answer 1

$geneValues = array(
    '0000' => 0,
    '0001' => 1,
    '0010' => 2,
    '0011' => 3,
    '0100' => 4,
    '0101' => 5,
    '0110' => 6,
    '0111' => 7,
    '1000' => 8,
    '1001' => 9,
    '1010' => '+',
    '1011' => '-',
    '1100' => '*',
    '1101' => '/');

$chromosome = '011010100111';
list($operand1, $operator, $operand2) = str_split($chromosome, 4);

switch($geneValues[$operator]) {
    case '+' : $result = $geneValues[$operand1] + $geneValues[$operand2]; break;
    case '-' : $result = $geneValues[$operand1] - $geneValues[$operand2]; break;
    case '*' : $result = $geneValues[$operand1] * $geneValues[$operand2]; break;
    case '/' : $result = $geneValues[$operand1] / $geneValues[$operand2]; break;
}
echo $result;

Answer 2

You think like I do.

In PHP, no you can't treat operators as data (without eval). If you try again in LISP you have a different story.
As all your operator are > 0x09, it is easy to detect them. If you wrote them as function pointers; rather than a piece of text, you could detect via is_callable() then execute them, passing the other items as data. This isn't hardcoding in that whatever you put in the function can be run. If you have no concern about performance, you can dynamically create the functions via create_function().
As a last option, you could use eval() e.g. eval() a text buffer containing all three genes. What you are doing doesn't have user input, so the normal security advisories don't apply.

If this was Perl, one would probably make the numbers function results in addition.

Have you thought about writing your initial genes out in decimal, or hex? It would be easier to read. When doing this you would need to use bit masks to pull the correct nibble out.

Answer 3

Have a look at eval. But be careful with it.

Example:

$value1 = 6;
$value2 = 3;
$operand = "-";
//$result will be 3
$result = eval("return (" . $value1 . $operand . $value2 . ");");