I have the following code:
if ($_POST['submit'] == "Next") {
foreach($_POST['info'] as $key => $value) {
echo $value;
}
}
How do I get the foreach function to start from the 2nd key in the array?
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12 Answers
For reasonably small arrays, use array_slice to create a second one:
foreach(array_slice($_POST['info'],1) as $key=>$value)
{
echo $value;
}
2 Comments
Clain Dsilva
Excellent use of array_slice superb
Ömer A.
How about ridiculously large arrays?
foreach(array_slice($_POST['info'], 1) as $key=>$value) {
echo $value;
}
Alternatively if you don't want to copy the array you could just do:
$isFirst = true;
foreach($_POST['info'] as $key=>$value) {
if ($isFirst) {
$isFirst = false;
continue;
}
echo $value;
}
2 Comments
James Anderson
I like the isFirst solution better. Its in your face logic, the array slice version could easily be missed when scanning unfamiliar code.
Ben Blank
The isFirst solution is also scales better with array size.
Couldn't you just unset the array...
So if I had an array where I didn't want the first instance, I could just:
unset($array[0]);
and that would remove the instance from the array.
1 Comment
Gareth Oates
In this scenario yes, but what if you wanted to do some comparison between the 2nd value in the array with the 1st value?
If you were working with a normal array, I'd say to use something like
foreach (array_slice($ome_array, 1) as $k => $v {...
but, since you're looking at a user request, you don't have any real guarantees on the order in which the arguments might be returned - some browser/proxy might change its behavior or you might simply decide to modify your form in the future. Either way, it's in your best interest to ignore the ordering of the array and treat POST values as an unordered hash map, leaving you with two options :
- copy the array and
unsetthe key you want to ignore - loop through the whole array and
continuewhen seeing the key you wish to ignore
1 Comment
Sean McSomething
From php.net/types.array : "An array in PHP is actually an ordered map". They act sorta strangely.
in loop:
if ($key == 0) //or whatever
continue;
2 Comments
xtofl
I tend to advise against testing for 'special cases' in a loop, if they are known upfront (i.e. the first entry) -> -1
Pedro Henrique
I don't the exact reason for @xtofl but for me, the problem is you have to test every time the loop runs if you are in the special case
Alternative way is to use array pointers:
reset($_POST['info']); //set pointer to zero
while ($value=next($_POST['info']) //ponter+1, return value
{
echo key($_POST['info']).":".$value."\n";
}
Comments
If you're willing to throw the first element away, you can use array_shift(). However, this is slow on a huge array. A faster operation would be
reset($a);
unset(key($a));
5 Comments
bobobobo
Really? How huge would
array_shift() become slow for? And why would unset be faster?
staticsan
Ya know, I can't remember why I answered this. Haven't needed this trick in a long time, but I probably got a speedup onceuponatime by doing it the other way! I would imagine an array of some tens of Mb in size might have a difference.
bobobobo
ACTUALLY!!
array_shift() is POISON!! It actually re-numbers all numerical array indices -- even if they are initially sparse (e.g. an array defined array(1=>'a', 3=>'b', 99=>'c') would become equivalent to array('0'=>'b', '1'=c) after an array_shift() operation. Don't array_shift() unless this is what you want!!bobobobo
And so yes, hence why this is faster. The re-indexing operation takes a lot of time.
staticsan
Well done for doing the research yourself. Just a note that sometimes the keys don't matter.
Working Code From My Website For Skipping The First Result and Then Continue.
<?php
$counter = 0;
foreach ($categoriest as $category) { if ($counter++ == 0) continue; ?>
It is working on opencart also in tpl file do like this in case you need.
Comments
On a array filled with 1000 elements the difference is quite minimal.
Test:
<?php
function slice($a)
{
foreach(array_slice($a, 1) as $key)
{
}
return true;
}
function skip($a)
{
$first = false;
foreach($a as $key)
{
if($first)
{
$first = false;
continue;
}
}
return true;
}
$array = array_fill(0, 1000, 'test');
$t1 = time() + microtime(true);
for ($i = 0; $i < 1000; $i++)
{
slice($array);
}
var_dump((time() + microtime(true)) - $t1);
echo '<hr />';
$t2 = time() + microtime(true);
for ($i = 0; $i < 1000; $i++)
{
skip($array);
}
var_dump((time() + microtime(true)) - $t2);
?>
Output:
float(0.23605012893677)
float(0.24102783203125)
if you structure your form differently
<input type='text' name='quiz[first]' value=""/>
<input type='text' name='quiz[second]' value=""/>
...then in your PHP
if( isset($_POST['quiz']) AND
is_array($_POST['quiz'])) {
//...and we'll skip $_POST['quiz']['first']
foreach($_POST['quiz'] as $key => $val){
if($key == "first") continue;
print $val;
}
}
...you can now just loop over that particular structure and access rest normally
1 Comment
strager
How about you use integers instead of strings? (Even though technically it's sent over as a string, it's easier to debug (and generate!) with integers.)
How about something like this? Read off the first key and value using key() and current(), then array_shift() to dequeue the front element from the arrayarray_shift(), it renumbers any numerical indices in the array, which you don't always want!).
<?php
$arr = array(
'one' => "ONE!!",
'two' => "TWO!!",
'three' => "TREE",
4 => "Fourth element",
99 => "We skipped a few here.."
) ;
$firstKey = key( $arr ) ;
$firstVal = current( $arr ) ;
echo( "OK, first values are $firstKey, $firstVal
" ) ;
####array_shift( $arr ) ; #'dequeue' front element # BAD! renumbers!
unset( $arr[ $firstKey ] ) ; # BETTER!
echo( "Now for the rest of them
" ) ;
foreach( $arr as $key=>$val )
{
echo( "$key => $val
" ) ;
}
?>
Comments
