array_slice with continuous sequence php - php

Question

Good Day!
I have array structure for 13 with range (1,13);
it something like
array(1,2,3,4,5,6,7,8,9,10,11,12,13);
$slice=2;
$ignore = 3;
i want array structure like array(3,4,5,8,9,10,13);
I tried with array_slice function but i couldn't offset the value sequentially
array_slice($array,2,13,true);
is there a way to ignore the next 3 values and add slice to the next second until last array, any native function or key will be great.
Thanks,
vicky

Answer 1

Using array_merge(), function one could join two array slice. This will return a new array.
http://php.net/manual/en/function.array-merge.php
<?php
$slice = 2;
$ignore = 3;
$a = array(1,2,3,4,5,6,7,8,9,10,11,12,13);
$a = array_merge(array_slice($a, $slice,$ignore),array_merge(array_slice($a, 2* $slice + $ignore,3), array_slice($a, 3* $slice + 2*$ignore)));
var_dump($a);
?>
I hope you got it. :)

Answer 2

Here's a function that will recursively perform an "asymmetric" slicing of an array of n length:
function slice_asym(array $head, $exclude, $include)
{
$keep = array_slice($head, $exclude, $include);
$tail = array_slice($head, $exclude + $include);
return $tail ? array_merge($keep, slice_asym($tail, $exclude, $include))
: $keep;
}
Recursion requires a base case where recursion stops and all scopes unwind and return. In our case, we want to stop when the tail contains no more elements.
array_slice() always returns an array - if there are no elements to return for its given offset, array_slice() returns an empty array. So, for each recursion, we want to:
Slice out the element(s) that we want to $keep
Create a $tail - this is a subset of the array that excludes the elements that we both want to ignore and keep in the current scope ($exclude + $include).
If the $tail is not empty, create a new level of recursion. Otherwise stop recursion and merge all current $keep elements with the result of the next level of recursion.
In pseudocode, this looks something like:
# step 1: first recursion
head = [1,2,3,4,5,6,7,8,9,10,11,12,13]
keep = [3,4,5]
tail = [6,7,8,9,10,11,12,13] # tail not empty
# step 2: second recursion
head = [6,7,8,9,10,11,12,13]
keep = [8,9,10]
tail = [11,12,13] # tail not empty
# step 3: third recursion
head = [11,12,13]
keep = [13]
tail = [] # tail empty: base case met!
# return and merge `keep` elements
[3,4,5] + [8, 9, 10] + [13] -> [3,4,5,8,9,10,13]
As per your example, the following invocation:
$range = range(1, 13); // [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13]
$sliced = slice_asym($range, 2, 3);
print_r($sliced);
Yields:
Array
(
[0] => 3
[1] => 4
[2] => 5
[3] => 8
[4] => 9
[5] => 10
[6] => 13
)
Edit
If you are using PHP version 5.5 or above, this is also a good use case for a generator.
These are useful because:
A generator allows you to write code that uses foreach to iterate over a set of data without needing to build an array in memory, which may cause you to exceed a memory limit, or require a considerable amount of processing time to generate.
So, you would not have to pre-create an array of sequential values:
Instead, you can write a generator function, which is the same as a normal function, except that instead of returning once, a generator can yield as many times as it needs to in order to provide the values to be iterated over.
We could implement a generator for your use case like so:
/**
*
* #param int $limit
* #param int $exclude
* #param int $include
* #return int
*/
function xrange_asym($limit, $exclude, $include) {
if ($limit < 0 || $exclude < 0 || $include < 0) {
throw new UnexpectedValueException(
'`xrange_asym` does not accept negative values');
}
$seq = 1;
$min = $exclude;
$max = $exclude + $include;
while ($seq <= $limit) {
if ($seq > $min && $seq <= $max) {
yield $seq;
}
if ($seq === $max) {
$min = $exclude + $max;
$max = $exclude + $include + $max;
}
$seq = $seq + 1;
}
}
and use it, like so:
foreach (xrange_asym(13, 2, 3) as $number) {
echo $number . ', '; // 3, 4, 5, 8, 9, 10, 13
}
Or use iterator_to_array() to generate the whole range as an array:
print_r(iterator_to_array(xrange_asym(13, 2, 3)));
Hope this helps :)