I've created a collection of variable variables using a foreach loop and I want to find out how many there are; and then select one with pseudo randomness.
Example code:
$count = 0;
foreach ($a as $key => $b) {
$count++;
$new_stuff["stuff" . $count] = $b;
}
extract($new_stuff);
I can then echo out each stuff, like this:
echo $stuff1[0];
or...
echo implode($stuff1); (this one gives me double the result)
I want to find out how many $stuff variables there are* and then pick one with one with rand(). Is it somehow possible to construct a variable from two parts, like this pseudocode: $stuff = "stuff" and attaching, say, number 5 so that it becomes $stuff5?
*I can find out the number of elements that create the various $stuff variables by using this:
$shift = rand(0, count($a));
array_rand is an option but rand() is not a very reliable random number generator.
Assuming your keys are numeric, it would be better to use mt_rand() with count().
$random = $a[ mt_rand(0, count($a)-1) ];
Related
I'm trying to create a random number generator in PHP. It's supposed to generate three (3) numbers at a time, without repeat. That's to say, the 3 numbers cannot be the same.
Here's what I've tried so far:
$array = [];
$A = mt_rand(1,36);
$array[0] = $A;
$B = mt_rand(1,36);
$array[1] = $B;
if(in_array($B,$array)){
$B = mt_rand(1,36);
$array[1] = $B;
}
$C = mt_rand(1,36);
$array[2] = $C;
if(in_array($C,$array)){
$C = mt_rand(1,36);
$array[2] = $C;
}
$length = count($array);
//display the array values;
for($i = 0; $i < $length; $i++){
echo ($array[$i]."<br>");
}
Can anyone tell me where I'm going wrong?
Like this ( as per my initial comment ),
$array = [];
while( count($array) < 3 ){
$rand = mt_rand(1,36);
$array[$rand] = $rand;
}
print_r( $array );
By setting the "key" to be the random number, we can abuse the fact that associative array keys are unique. Then it's a simple matter of waiting until the array contains the desired amount of unique items.
You can test it here
Outputs: ( your results may vary, it's random )
Array
(
[16] => 16
[20] => 20
[27] => 27
)
UPDATE I was trying to think of a valid way to do it without using a loop ( on my way home from work ), and this way may be even better in some cases.
$a = range(1,36);
shuffle($a);
$array = array_slice($a, 0, 3);
print_r($array);
This will have better performance when the number of items you must find is higher. This is because there is no repetition, no collisions. So if you have a small range but need to find many items for the return, this will preform better. If you have many items and need to return only few, then the first one may be better, if not from speed then from memory use.
You can see it here
For reference this uses
range() - Create an array containing a range of elements.
http://php.net/manual/en/function.range.php
shuffle() - Shuffles (randomizes the order of the elements in) an array. It uses a pseudo random number generator that is not suitable for cryptographic purposes.
http://php.net/manual/en/function.shuffle.php
array_slice() - Returns the sequence of elements from the array as specified by the offset and length parameters.
http://php.net/manual/en/function.array-slice.php
So to explain this last one
First we create an array that contains each of our possible numbers as an element. So for example like this [1,2,3,4,5,6, ...].
Next we shuffle it which randomizes the order of the whole array. Shuffle modifies the array by "reference" so it doesn't return our array and therefor there is no assignment ( I think it returns Boolean, however I'm at a loss as to how it could fail and return false, pretty much it just returns true which we don't want to overwrite our array with ). So our example then becomes this [16,20,27,14,5,1, ...]
Last we cut out the number of items we need to return. Finally we end the example with this [16,20,27];
You can crunch the first one down into one ( really 2) line by assigning the value of the $rand variable in the condition of the loop. Like this:
$array = [];
while( count($array) < 3 && false !== ($rand = mt_rand(1,36))) $array[$rand] = $rand;
Because mt_rand(1,36) will never return boolan false. Also if I remember mt_rand is the same as rand now, or at least in current PHP versions.
Note: As of PHP 7.1.0, rand() uses the same random number generator as mt_rand(). To preserve backwards compatibility rand() allows max to be smaller than min as opposed to returning FALSE as mt_rand(). http://php.net/manual/en/function.rand.php
Hope it helps you, remember to think outside of the box.
I'm trying to make a simple PHP script for school. I need to output 2 random students from the array $leerlingen (Leerlingen = students).
It work's fine when I use echo $leerlingen within the foreach loop, but when I use the return statement it stops executing, because when return is used, it ends the function.
Code:
$leerlingen = array("tobias", "hasna", "aukje", "fred", "sep", "koen", "wahed", "anna", "jackie", "rashida", "winston", "sammy", "manon", "ben", "karim", "bart", "lisa", "lieke");
shuffle($leerlingen);
function maakGroepjes($leerlingen) {
$begin = 1;
foreach ($leerlingen as $leerling) {
if ($begin <= 2) {
echo $leerling;
$begin++;
}
}
}
echo maakGroepjes($leerlingen);
Can anyone tell me how to solve this problem?
You can return only one value inside a function, in this case is an array. I assume that the array have at least two values.
<?php
$leerlingen = array(
"tobias", "hasna", "aukje", "fred", "sep", "koen", "wahed", "anna", "jackie", "rashida", "winston", "sammy", "manon", "ben", "karim", "bart", "lisa", "lieke"
);
shuffle($leerlingen);
function maakGroepjes($leerlingen) {
//your result array
$result = array();
//Picking 2 random entries out of an array to $keys
$keys = array_rand($leerlingen, 2);
//Returning the array with two values
return array($leerlingen[$keys[0]], $leerlingen[$keys[1]]);
}
//assign the values to the vars
list($one, $two) = maakGroepjes($leerlingen);
//printing
echo $one . "<br>\n";
echo $two . "<br>\n";
?>
array_rand and other functions (rand) that rely on libc have a bad standard distribution. I'd always recommend using mt_rand() if you need it to be equally distributed, otherwise some entries will be heavily favored.
This is a good easy replacement for numerical arrays:
function array_mt_rand($array) {
return $array[ mt_rand( 0, count($array)-1 ) ];
}
$one = array_mt_rand($array);
$two = array_mt_rand($array);
You may need some extra checks if you have a small array and always want two distinct values though.
You could always try something like this.
function maakGroepjes($leerlingen) {
do {
$first_student = array_rand($leerlingen);
$second_student = array_rand($leerlingen);
} while ($leerlingen[$first_student] == $leerlingen[$second_student]);
return [$leerlingen[$first_studen], $leerlingen[$second_student]];
}
Which returns this.
Array
(
[0] => manon
[1] => winston
)
Also, the difference between a function printing/echo'ing information and returning information is pretty big.
You can't assign a variable to the echo statement inside of a function, whereas you could assign a variable to the return statement.
I would approach this a little differently.
function maakGroepjes($leerlingen) {
shuffle($leerlingen); // randomize the list of students
return array_chunk($leerlingen, 2); // break in into groups of two and return it
}
Then with
$groepjes = maakGroepjes($leerlingen);
you can generate all of the groups at once. No worries about repetition. This way if you need multiple groups, you can loop over the list of groups. If you really only need one group of two, then that will be
$groepjes[0];
which you can ouptut however you like. A very simple example:
foreach ($groepjes[0] as $student) echo "$student<br>";
Try this:
if ($begin <= 2) {
echo $leerling;
$begin++;
} else {
return
}
What this does is: every time through the loop, it looks at $begin. If it's less than or equal to two, it echoes that student and increments $begin. Otherwise, if it's greater than two, it returns, ending the function (and thus, the loop).
A perhaps better way to do it would be to just look at the ordinal directly:
foreach ($leerlingen as $ord => $leerling) {
echo $leerling;
if ($ord == 1) return;
}
Note the syntax in the loop definition. The "old =>" part sets the ordinal value as a variable as you loop through, letting you see which entry in the array you are currently on. So, this just loops through printing students. When it has printed the second student (remember, arrays are counted 0, 1, 2...) it returns.
Also, you probably don't want to echo maakGroepjes(). That function is what is echoing the student names. You probably don't want to echo the function result unless the function compiles the names into a string and returns the string or something.
I am not sure if its a good idea, but i just thought it would be less tedious and much easier to declare variables on the fly using a for loop:
$val.$i = $row1[$i];. Now after trying this, this obviously isn't the right thing to do. Is there anyway i can improve this and not declare separate variables.
Maybe this will give a clearer picture:
for($i = 1; $i < 5; $i++) {
$val.$i = $row1[$i];
}
Now i want to achieve $val1 using $val.$i.
As others have posted, using an associative or 0-based array would be a far better implementation, but you can implement the solution just as you have requested using PHP's variable variable names:
for ($i = 1; $i <= 5; $i++)
{
${"val".$i} = "this is value " . $i;
}
echo "$val1<br />$val2<br />$val3<br />$val4<br />$val5";
Will output:
this is value 1
this is value 2
this is value 3
this is value 4
this is value 5
In PHP you can define variables by name.
Example:
$foo = 'bar';
$$foo = 'baz';
echo $bar; // echoes 'baz'
So in your case, it would look like:
$var = 'val'.$i;
$$var = $arr[$i];
Why you would do that, I have no idea.
A better system (imho) is to use list() construct:
list($val1, $val2, $val3) = $arr;
You could create an associative array and then use extract:
$arr = array();
// ...
$arr[$val.$i] = $row1[$i];
// ...
extract($arr);
Mind you, it will probably be better to use the array in the first place.
I believe you're trying to get all the data you are reading from your database into one easy to access place. All you need to do is shove each row into an array:
$allTheThings[] = $row1;
You'll end up with a two dimensional array where the first key is the row number and the second key is the column number.
I am not getting full picture of what you are trying to do, but to convert arrays into objects you would do this:
$val = (object) $row1;
$index = 0;
foreach ($sxml->entry as $entry) {
$array + variable index number here = array('title' => $title);
$index++;
}
I'm trying to change an array name depending on my index count. Is it possible to change variable name (ie. $array1, $array2 $array3 etc.) in the loop?
Edit:
After the loop has finished, I will generate a number number (depending on the count of $index) and then use this array... probably it's a stupid way of accomplishing what Im trying to do, but I don't have a better idea.
You might want to try this instead:
$index = 0;
$arrays = array();
foreach ($sxml->entry as $entry) {
$arrays[$index] = array('title' => $title);
$index++;
}
While it is technically possible to do what you are asking, using an array of arrays will probably work better from you.
This type of indexing is exactly what arrays are designed for, you have a lot of items and want to be able to refer to them by number.
Unless you have a very specific reason to use the name of the variable to represent it's number you will probably have a much simpler time using it's index in the outer array.
Yes you can user an associate array. Generating a string dynamically based on the iteration number and using that as a key in the array.
You can use variable variables. php.net
PHP supports Variable variables:
$num = 1;
$array_name = 'array' . $num;
$$array_name = array(1,2,3);
print_r($array1);
http://php.net/manual/en/language.variables.variable.php
I have some numbers which will be part of an sql query, like this...
152258, 152258, 152258, 152258, 152261, 152261, 152261, 152261, 152261, 152270,
152270, 152270, 152287, 152287, 152287, 152287
My query is quite complex and the list is quite long and I need to produce a unique list of numbers, can I do this with a regex?
If not how ?
Here is how you can make your string have unique numbers:
http://codepad.org/cziNtZOS
<?php
$myString = "152258,152258,152258,152258,152261,152261,152261,152261,152261,152270,152270,152270,152287,152287,152287,152287";
$array = explode(",",$myString);
$unique = array_unique ( $array );
$myUniqueString = implode(",",$unique);
echo $myUniqueString ;
?>
I was going to write a function for you, turns out PHP has one already: array_unique()
Edit: in any case, this is one of the alternative ways of doing it:
function uniquify_array($a)
{
$b = array(); // I wish I could write just $b = {};
foreach ($a as $i)
$b[$i] = $i;
return $b;
}
Note that this function works only with values, whereas the built-in array_unique() preserves the keys in the original array.
Generate some set of numbers and then just use array_unique function
$nums = array();
for ($i = 0; $i < $limit; $i++) {
$nums[] = rand() * 10000;
$nums = array_unique($nums);
}
Sultan
If you want a range of numbers use PHP's range() method
If you want a unique list of numbers, you can use PHP's rand() method
range() : http://php.net/manual/en/function.range.php
rand() : http://php.net/manual/en/function.rand.php
EDIT
And as #RobertPitt points out, uniqid can be used for generating IDs as well : http://php.net/manual/en/function.uniqid.php
USE RANGE()
REFERENCE