Determine if the array has negative numbers and change them to zero - php

Question

I have wrote this code:
$final = array(
($data[0] - $data[1]),
($data[1] - $data[2]),
($data[2] - $data[3]),
($data[3] - $data[4]),
($data[4] - $data[5]),
($data[5] - $data[6])
);
Some of them will return negative numbers (-13,-42 etc...), how to change the negative ones to 0?
By the way the think i do after is:
$data_string = join(",", $final);
Example: I need to convert it like in the following:
1,3,-14,53,23,-15 => 1,3,0,53,23,0

Answer 1

You can map that:
$zeroed = array_map(function($v) {return max(0, $v);}, $final);
Will set all numbers lower than 0 to 0.
See array_map and max.
Additionally, you can save you some more handwriting with $data:
$final = array_reduce($data, function($v, $w)
{
static $last;
if (null !== $last) $v[] = max(0, $last - $w);
$last = $w;
return $v;
}, array());
$data_string = join(",", $final);
See array_reduce.
Edit: A foreach loop might be easier to follow, I added some comments as well:
// go through all values of data and substract them from each other,
// negative values turned into 0:
$last = NULL; // at first, we don't have a value
$final = array(); // the final array starts empty
foreach($data as $current)
{
$isFirst = $last === NULL; // is this the first value?
$notFirst = !$isFirst;
if ($notFirst)
{
$substraction = $last - $current;
$zeroed = max(0, $substraction);
$final[] = $zeroed;
}
$last = $current; // set last value
}
And here is the demo.

Answer 2

Am guessing this is homework. If so please mark it as such.
Hints:
use a loop instead of hardwired array references.
use an if-statement to check for negative values and switch their sign.
your use of join is correct

Answer 3

I like Hakre's compact answer. However, if you have a more complex requirement, you can use a function:
<?php
$data = array(11,54,25,6,234,9,1);
function getZeroResult($one, $two) {
$result = $one - $two;
$result = $result < 0 ? 0 : $result;
return $result;
}
$final = array(
getZeroResult($data[0], $data[1]),
getZeroResult($data[1], $data[2]),
getZeroResult($data[2], $data[3]),
getZeroResult($data[3], $data[4]),
getZeroResult($data[4], $data[5]),
getZeroResult($data[5], $data[6])
);
print_r($final);
?>
http://codepad.org/viGBYj4f (With an echo to show the $result before test.)
Which gives you:
Array
(
[0] => 0
[1] => 29
[2] => 19
[3] => 0
[4] => 225
[5] => 8
)
Note, you could also just return the ternary:
function getZeroResult($one, $two) {
$result = $one - $two;
return $result < 0 ? 0 : $result;
}
As well as using it in a loop:
<?php
$data = array(11,54,25,6,234,9,1);
function getZeroResult($one, $two) {
$result = $one - $two;
echo "$one - $two = $result\n";
return $result < 0 ? 0 : $result;
}
$c_data = count($data)-1;
$final = array();
for ($i = 0; $i < $c_data; $i++) {
$final[] = getZeroResult($data[$i], $data[$i+1]);
}
print_r($final);
?>
http://codepad.org/31WCbpNr