Multidimensional sub array subtraction in PHP - php

Question

Need subarray difference of below array
$arr = array(
array('s'=>'1','e'=>'3'),
array('s'=>'6','e'=>'7'),
array('s'=>'8','e'=>'9'),
array('s'=>'10','e'=>'14'),
array('s'=>'16','e'=>'17'),
)
if(arr[$arr[$i+1][s] - $i][e] <= 1){
//join them
}
else {
//save them as it is
}
Desired result should
$arr = array(
array('s'=>'1','e'=>'3'),
array('s'=>'6','e'=>'14'),
array('s'=>'16','e'=>'17'),
)
No consecutive (next S-E) should be 1
http://codepad.org/V8omMdn6 is where im struck at
See its like
iteration 0
6-3 = 3
so save array('s'=>'1','e'=>'3'),
iteration 1
8-7 = 1
array('s'=>'6','e'=>'9'), => discade in 2 as it
iteration 2
10-9 = 1
array('s'=>'6','e'=>'10'), => discade in 3 as it
iteration 3
10-9 = 1
array('s'=>'6','e'=>'14'),
iteration 4
16-14 = 4
array('s'=>'16','e'=>'17'),

Answer 1

$result = [];
foreach ($arr as $pair) {
if (empty($result) || $pair['s'] - end($result)['e'] > 1) {
$result[] = $pair;
} else {
$result[key($result)]['e'] = $pair['e'];
}
}
You might also use $last as key instead end() & key() for readability.
Using array pointer functions on $result shortens the code but uses some ugly hidden effects. end($result) returns last element of array (using key bracket with function result is possible since php5.3 I guess), but also sets the pointer, so key($result) will return correct key if needed.
While iterating you process last element of result array - this element might not be valid right away, but you don't need to look ahead. There are two scenarios for last element (+initial state condition for empty $result):
invalid: set e value from current item and process further
valid: leave it and push current item into results for further validation (unless that was the last one).

Answer 2

I took a very brief look at your codepen, I think what you want to achieve is to find out if the start time of a new session is within a given period from the end time of the last session, if so you would like to combine those sessions.
I think you confused yourself by trying to subtract start time of new session from end time of last session, it should be the other way round.
The way you worded the question made it even more confusing for people to understand.
If my interpretation of your question is correct, the below code should work with the test case you posted here.
function combineSession($arr){
$arrCount=count($arr)-1;
for ($i=0; $i<$arrCount; $i++){
//if the difference between s and e is less than or equal to one, then there is a consecutive series
if($arr[$i+1]['s']-$arr[$i]['e'] <= 1){
//assign the value of s at the start of a consecutive series to $temp
if (!isset($temp)){
$temp=$arr[$i]['s'];
}
//if consecutive series ends on the last sub_array, write $temp e pair to output
if ($i==$arrCount-1){
$output[]= array('s'=> $temp, 'e' => $arr[$arrCount]['e']);
}
}
//end of a consecutive series, write $temp and e pair to output, unset $temp
else if (isset($temp) && $i<$arrCount-1){
$output[]=array('s'=> $temp, 'e' => $arr[$i]['e']);
unset($temp);
}
//consecutive series ended at the second last sub-array, write $temp and e pair to output and copy key value pair of the last sub-array to output
else if ($i==$arrCount-1){
$output[]=array('s'=> $temp, 'e' => $arr[$i]['e']);
$output[]=$arr[$arrCount];
}
//not in a consecutive series, simply copy s e key value pair to output
else {
$output[]=$arr[$i];
}
}//end of for loop
print_r($output);
}//end of function

Answer 3

else if ($i==$arrCount-1){ $output[]=!isset($temp) ? $arr[$i] : array('s'=> $temp, 'e' => $arr[$i]['e']); $output[]=$arr[$arrCount]; }