PHP random numbers frequency of occurrence - php

Question

In PHP I want to generate random numbers from 1 to 10 in a loop.
So for example:
$factor="1"; // this will be changed in another area
for ($i=0;$i<10;$i++) {
if ($factor=="1") {$output = rand(1,10);}
else if ($factor=="2") {$output = rand(1,10);}
else {$output = rand(1,10);}
}
Now to explain this - In result I want to receive 10 random numbers, but when $factor = "2", in that case I want to receive numbers from 6 to 10 more frequently as lower numbers.
It means, from 10 numbers I need to have 80% higher random numbers (it means larger than 5) and in 20% lower numbers (5 or lower).
E.g. 1,2,6,7,8,9,7,9,8,6 (1,2 are the only lower numbers = 20%, the rest are higher = 80)
If the $factor will change, then I want to change the percentage, in that case for example 40% lower numbers, 60% higher numbers.
The idea I have is to put each output in the loop to an array, then check each result and somehow calculate, if there is no 80% of larger numbers, then get random numbers again for those, but this seems to be an overkill.
Is there a simplier solution?

Answer 1

Let's go with the percentages you mention and first generate a random number between 1 and 100. Then the lower number, 1 to 20, have to represent outputs 1 to 5 and the higher numbers, 21 to 100, have to represent output 6 to 10. In PHP that would look like this:
function HighMoreOften()
{
$percentage = rand(1, 100);
if ($percentage <= 20) {
return rand(1, 5);
} else {
return rand(6, 10);
}
}
That should do the trick. You can also convert the percentage you got into the output, this would probably be slightly faster:
function HighMoreOften()
{
$percentage = rand(1, 100);
if ($percentage <= 20) {
return ceil($percentage / 5);
} else {
return 6 + ceil(($percentage - 20) / 20);
}
}
but personally I think the first version is easier to understand and change.

Answer 2

To change frequency you gonna need an array of numbers. And a sum to this direction. frequency is the relation of something between an array of things.
$t = 0;
// $factor = 1; // let's say that this means 20%
$factor = 2; // let's say that this means 40%
if ($factor === 1) {
for ($i = 1; $i <= 80; $i++) {
$t += rand(1,10);
}
for ($i = 1; $i <= 20; $i++) {
$t += rand(6,10);
}
} else if ($factor === 2) {
for ($i = 1; $i <= 60; $i++) {
$t += rand(1,10);
}
for ($i = 1; $i <= 40; $i++) {
$t += rand(6,10);
}
} else {
for ($i = 1; $i <= 100; $i++) {
$t += rand(1,10);
}
}
echo round(($t/100), 0);
Something like that! :)

Answer 3

I came with a very simple (maybe creepy) solution, but this works as I wanted:
echo print_r(generate("2"));
function generate($factor) {
$nums=array();
for ($i=0;$i<10;$i++) {
if ($i<$factor) {$rnd = rand(1,5);}
else {$rnd = rand(6,10);}
array_push($nums,$rnd);
}
return $nums;
}
I can also shuffle the final array results, as the lower numbers will be on the beginning always, but in my case it doesn't matter.