In Python, there exists a Counter class that allows me to do this:
counter = Counter()
counter[2] = 5
counter[3] = 2
for i in range(5):
print(f'counter[{i}]={counter[i]}')
Which will give me the following output:
counter[0]=0
counter[1]=0
counter[2]=5
counter[3]=2
counter[4]=0
Basically it acts as if any element in the dictionary that has not been explicitly initialized has the value of zero, and will never throw an exception when accessing non-existing element.
Is there a similar entity in PHP, or is the only way to check each index when accessing in a loop?
I am looking for a way to avoid doing this:
for ($i = 0; $i < numOfSomeResults; $i++) {
if (isset($otherResult[$i]) {
echo $otherResult[$i];
} else {
echo "0";
}
}
And do something like:
for ($i = 0; $i < $numOfSomeResults; $i++) {
echo $counter[i];
}
Both the indexes and values I need to work with are integers if that helps.
Without reinventing the wheel and following on from Alex's comment, you can use the null coalescing operator (PHP 7+)
for ($i = 0; $i < $numOfSomeResults; $i++) {
echo $counter[$i] ?? 0;
}
Some background information about what it does:
The null Coalescing operator is mainly used to avoid the object function to return a NULL value rather returning a default optimized value. It is used to avoid exception and compiler error as it does not produce E-Notice at the time of execution.
(Condition) ? (Statement1) ? (Statement2);
This same statement can be written as:
if ( isset(Condition) ) {
return Statement1;
} else {
return Statement2;
}
Try this:
Put '$' in front of 'i'. The code below must work.
for ($i = 0; $i < numOfSomeResults; $i++) {
if (isset($otherResult[$i]) {
echo $otherResult[$i];
} else {
echo 0;
}
}
Related
I have this code:
<?php
function generator() {
yield 'First value';
for ($i = 1; $i <= 3; $i++) {
yield $i;
}
}
$gen = generator();
$first = $gen->current();
echo $first . '<br/>';
//$gen->next();
foreach ($gen as $value) {
echo $value . '<br/>';
}
This outputs:
First value
First value
1
2
3
I need the 'First value' to yielding only once. If i uncomment $gen->next() line, fatal error occured:
Fatal error: Uncaught exception 'Exception' with message 'Cannot rewind a generator that was already run'
How can I solve this?
The problem is that the foreach try to reset (rewind) the Generator. But rewind() throws an exception if the generator is currently after the first yield.
So you should avoid the foreach and use a while instead
$gen = generator();
$first = $gen->current();
echo $first . '<br/>';
$gen->next();
while ($gen->valid()) {
echo $gen->current() . '<br/>';
$gen->next();
}
chumkiu's answer is correct. Some additional ideas.
Proposal 0: remaining() decorator.
(This is the latest version I am adding here, but possibly the best)
PHP 7+:
function remaining(\Generator $generator) {
yield from $generator;
}
PHP 5.5+ < 7:
function remaining(\Generator $generator) {
for (; $generator->valid(); $generator->next()) {
yield $generator->current();
}
}
Usage (all PHP versions):
function foo() {
for ($i = 0; $i < 5; ++$i) {
yield $i;
}
}
$gen = foo();
if (!$gen->valid()) {
// Not even the first item exists.
return;
}
$first = $gen->current();
$gen->next();
$values = [];
foreach (remaining($gen) as $value) {
$values[] = $value;
}
There might be some indirection overhead. But semantically this is quite elegant I think.
Proposal 1: for() instead of while().
As a nice syntactic alternative, I propose using for() instead of while() to reduce clutter from the ->next() call and the initialization.
Simple version, without your initial value:
for ($gen = generator(); $gen->valid(); $gen->next()) {
echo $gen->current();
}
With the initial value:
$gen = generator();
if (!$gen->valid()) {
echo "Not even the first value exists.<br/>";
return;
}
$first = $gen->current();
echo $first . '<br/>';
$gen->next();
for (; $gen->valid(); $gen->next()) {
echo $gen->current() . '<br/>';
}
You could put the first $gen->next() into the for() statement, but I don't think this would add much readability.
A little benchmark I did locally (with PHP 5.6) showed that this version with for() or while() with explicit calls to ->next(), current() etc are slower than the implicit version with foreach(generator() as $value).
Proposal 2: Offset parameter in the generator() function
This only works if you have control over the generator function.
function generator($offset = 0) {
if ($offset <= 0) {
yield 'First value';
$offset = 1;
}
for ($i = $offset; $i <= 3; $i++) {
yield $i;
}
}
foreach (generator() as $firstValue) {
print "First: " . $firstValue . "\n";
break;
}
foreach (generator(1) as value) {
print $value . "\n";
}
This would mean that any initialization would run twice. Maybe not desirable.
Also it allows calls like generator(9999) with really high skip numbers. E.g. someone could use this to process the generator sequence in chunks. But starting from 0 each time and then skipping a huge number of items seems really a bad idea performance-wise. E.g. if the data is coming from a file, and skipping means to read + ignore the first 9999 lines of the file.
solutions provided here does not work if you need to iterate more than once.
so I used iterator_to_array function to convert it to array;
$items = iterator_to_array($items);
I can't figure out how to test if there's a next item in my array by using the key to test against. I think this is better explained in code. I know there's an easier way, I'm just a noob!
Basically I want to know if there is another item in the array and if so get the ->comp_id value.
for($i=0; $i<count($allcomps); $i++)
{
if($allcomps[$i]->comp_id == $curCompID)
{
$currentIndex = $i;
if($allcomps[$i+1]->comp_id == null )
{
echo "there isn't a next";
}
//echo $allcomps[$currentIndex+1]->comp_id;
}
}
You're already looping through allcomps, so why do you need a check for the next one?
Why not check within the loop?
for($i=0; $i<count($allcomps); $i++) {
if (isset($allcomps[$i]->comp_id) and $allcomps[$i]->comp_id == $curCompID) {
$currentIndex = $i;
}
}
I think a foreach might be even easier:
foreach($allcomps as $i=>$comp) {
if (isset($comp->comp_id) and $comp->comp_id == $curCompID) {
$currentIndex = $i;
}
}
I'm using json_decode to parse JSON files. In a for loop, I attempt to capture specific cases in the JSON in which one element or another exist. I've implemented a function that seems to fit my needs, but I find that I need to use two for loops to get it to catch both of my cases.
I would rather use a single loop, if that's possible, but I'm stuck on how to get both cases caught in a single pass. Here's a mockup of what I would like the result to look like:
<?php
function extract($thisfile){
$test = implode("", file($thisfile));
$obj = json_decode($test, true);
for ($i = 0; $i <= sizeof($obj['patcher']['boxes']); $i ++) {
//this is sometimes found 2nd
if ($obj['patcher']['boxes'][$i]['box']['name'] == "mystring1") {
}
//this is sometimes found 1st
if ($obj['patcher']['boxes'][$i]['box']['name'] == "mystring2") {
}
}
}
?>
Can anyone tell me how I could catch both cases outlined above within a single iteration?
I clearly could not do something like
if ($obj['patcher']['boxes'][$i]['box']['name'] == "string1" && $obj['patcher']['boxes'][$i]['box']['name'] == "string2") {}
...because that condition would never be met.
Generally what I do when I have raw data that is in an order that isn't ideal to work with is to run a first loop pass to generate a a list of indexes for me to pass through a second time.
So a quick example from your code:
<?php
function extract($thisfile){
$test = implode("", file($thisfile));
$obj = json_decode($test, true);
$index_mystring2 = array(); //Your list of indexes for the second condition
//1st loop.
$box_name;
for ($i = 0; $i <= sizeof($obj['patcher']['boxes']); $i ++) {
$box_name = $obj['patcher']['boxes'][$i]['box']['name'];
if ( $box_name == "mystring1") {
//Do your code here for condition 1
}
if ($box_name == "mystring2") {
//We push the index onto an array for a later loop.
array_push($index_mystring2, $i);
}
}
//2nd loop
for($j=0; $j<=sizeof($index_mystring2); $j++) {
//Your code here. do note that $obj['patcher']['boxes'][$j]
// will refer you to the data in your decoded json tree
}
}
?>
Granted you can do this in more generic ways so it's cleaner (ie, generate both the first and second conditions into indexes) but i think you get the idea :)
I found that something like what #Jon had mentioned is probably the best way to attack this problem, for me at least:
<?php
function extract($thisfile){
$test = implode("", file($thisfile));
$obj = json_decode($test, true);
$found1 = $found2 = false;
for ($i = 0; $i <= sizeof($obj['patcher']['boxes']); $i ++) {
//this is sometimes found 2nd
if ($obj['patcher']['boxes'][$i]['box']['name'] == "mystring1") {
$found1 = true;
}
//this is sometimes found 1st
if ($obj['patcher']['boxes'][$i]['box']['name'] == "mystring2") {
$found2 = true;
}
if ($found1 && $found2){
break;
}
}
}
?>
Could anyone help me.
I need to return multiple img's, but with this code, only one of two is returning.
What is the solution.
Thank you in advance.
$test = "/claim/img/box.png, /claim/img/box.png";
function test($test)
{
$photo = explode(',', $test);
for ($i = 0; $i < count($photo); $i++)
{
$returnas = "<img src=".$photo[$i].">";
return $returnas;
}
}
This might be a good opportunity to learn about array_map.
function test($test) {
return implode("",array_map(function($img) {
return "<img src='".trim($img)."' />";
},explode(",",$test)));
}
Many functions make writing code a lot simpler, and it's also faster because it uses lower-level code.
While we're on the subject of learning things, PHP 5.5 gives us generators. You could potentially use one here. For example:
function test($test) {
$pieces = explode(",",$test);
foreach($pieces as $img) {
yield "<img src='".trim($img)."' />";
}
}
That yield is where the magic happens. This makes your function behave like a generator. You can then do this:
$images = test($test);
foreach($images as $image) echo $image;
Personally, I think this generator solution is a lot cleaner than the array_map one I gave earlier, which in turn is tidier than manually iterating.
Modify your code that way
function test($test)
{
$returnas = '';
$photo = explode(',', $test);
for ($i = 0; $i < count($photo); $i++)
{
$returnas .= "<img src=".$photo[$i].">";
}
return $returnas;
}
Your code didn't work since you were returning inside the loop immediatly. Every programming language support "only a return for call". In my solution you're appendig a string that has an img tag each time you enter the loop and return it after every photo is "passed" into the loop
You could even use the foreach() construct, of course
Bonus answer
If you don't know the difference between ...
for ($i = 0; $i < count($photo); $i++)
and
for ($i = 0, $count = count($photo); $i < $<; $i++)
Well, in first case you'll evaluate count($photo) every single time the for is called whereas the second time, it is evaluated only once.
This could be used for optimization porpuses (even if php, internally, stores the length of an array so it is accesible in O(1))
The function breaks after the first return statement. You need to save what you want to return in some structure, an array eg, and return this.
function test($test)
{
$result = array();
$photo = explode(',', $test);
for ($i = 0; $i < count($photo); $i++)
{
$returnas = "<img src=".$photo[$i].">";
$result[] = $returnas;
}
return $result;
}
I am simply trying to remove all of the Array objects that have 'visible' set to '0'
Array:
{
"Count":5,
"0":{"id":"1","visible":"0"},
"1":{"id":"3","visible":"0"},
"2":{"id":"1","visible":"0"},
"3":{"id":"2","visible":"0"},
"4":{"id":"3","visible":"0"}
}
PHP:
function cleanup($arr) {
for($i = 0; $i < (count($arr)-1); $i++) {
if($arr[$i]['visible'] == false) {
unset($arr[$i]);
}
}
$newarr = array_unique($arr, SORT_REGULAR);
$newarr['Count'] = count($newarr)-1;
return $newarr;
}
Result:
{
"Count":2,
"3":{"id":"2","visible":"0"},
"4":{"id":"3","visible":"0"}
}
In my mind this should work and return {"Count":0}. Also Why have the 'keys' not been set to 0,1 instead of 3,4. Where am i going wrong?
You are using count($arr)-1) inside the for loop, and it gets re-evaluated every iteration, so after you unset the first three times, i is 3, but count($arr)-1) is 1, and you exit the loop.
You should set $j=count($arr)-1 before the for loop, and use for($i = 0; $i < $j; $i++)
In general it is bad programming practice (performance-wise) to use functions like count() inside the for loop
unset() will not reorder the array indexes if you removing an index from the middle of an numerical array. You need to reindex the array by yourself. array_values() is helpful here.
function cleanup($arr) {
for($i = 0; $i < (count($arr)-1); $i++) {
if($arr[$i]['visible'] == false) {
unset($arr[$i]);
}
}
$newarr = array_values(array_unique($arr, SORT_REGULAR));
return $newarr;
}
The Count property makes no sense for me therefore I dropped it away. You may use the function count() instead.