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Php foreach key value reference

Summary : in this tutorial, you will learn how to use PHP foreach loop statement to loop over elements of an array or public properties of an object. PHP provides the foreach loop statement that allows you to iterate over elements of an array or public properties of an object.

The foreach loop statement only works with arrays and objects. If you use the foreach loop statement with other data typesyou will get an error. See the following example:. To change the values of array elements inside the loop, you have to use a reference that returns by the foreach loop. The following example demonstrates how the change values of elements of an indexed array inside the loop:.

To fix the problem, you should always reset the reference variable after the loop using the unset function as follows:. PHP foreach — iterate over elements of an associative array To loop over elements of an associative array, you use the following syntax:.

In this tutorial, you have learned how to use the PHP foreach statement to iterate over elements of indexed arrays, associative arrays, and public properties of an object.

php foreach key value reference

ZenTut Programming Made Easy. PHP foreach. PHP foreach — looping over elements of an indexed array To loop over elements of an indexed array, you use the following syntax:. Was this tutorial helpful? Yes No. Return to top of page. All Rights Reserved.The foreach construct provides an easy way to iterate over arrays. It is possible to customize object iteration. In that case the value will be assigned by reference. It is recommended to destroy it by unset. Otherwise you will experience the following behavior:.

Note : foreach does not support the ability to suppress error messages using. It is possible to iterate over an array of arrays and unpack the nested array into loop variables by providing a list as the value.

Submit a Pull Request Report a Bug. Notice: Undefined offset: 2 in example. Even though it is not mentioned in this article, you can use "break" control structure to exit from the "foreach" loop. Lots of people think the answer is two because it uses "reference to value, which it doesn't have to copy each value when it loops".

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Well, that's totally wrong! The array itself wasn't passed by reference to the function, so PHP knows that it isn't allowed to modify the outside array, so it therefore makes a copy of the array's internal iteration offset state that's just a simple number which says which item you are currently at during things like foreachwhich costs almost no performance or memory at all since it's just a small number.

That's what MANY people think. But the answer is NO. It re-uses the existing value in memory. With zero performance cost. Alright, so what's the second version doing? The beloved "iterate values by reference"? The array itself wasn't passed by reference to the function, so PHP knows that it isn't allowed to modify the outside array. If we just give them references to the original array's values, and they assign some new value to their reference, they would destroy the original array which they aren't allowed to touch!

It's almost always BAD! With worse performance, and risks of bugs and quirks as is demonstrated in the manual. Enjoy and good luck with your code! What happened to this note: "Unless the array is referenced, foreach operates on a copy of the specified array and not the array itself.

PHP foreach pass-by-reference: Do it right, or better not at all.

Don't rely on the array pointer during or after the foreach without resetting it. So on the three repetitions of the second "foreach" the array will look like: 1. I want just to mention that John is not entirely true. You just need to know well what are you doing.

Best of luck and happy coding all. If the key is on the other hand a string that can be type-juggled into a float, it will stay a string. Observed on PHP 7. It is not documented, but when modifying the array within foreach: PHP seems to create a snapshot, or a copy of the entire array "copy on write"?

Having to unset the reference manually completely destroys the practicality of using a referenced variable. This is a decent, simple, and easy way to reference other values of an associative array when using foreach.

The only care that needs to be taken is if the array is HUGE in size, so you don't run into memory use problems. The array is then copied using a foreach loop to make a duplicate array where the key and value order correspond to the first array, but the keys are sequential numeric starting at zero.Join Stack Overflow to learn, share knowledge, and build your career.

Connect and share knowledge within a single location that is structured and easy to search. I want to change the content of the original array, since i am returning this, but how do I get the name of the current array names in this example in my foreach loop? I recommend not using it unless you know why you need it and test the results. Thus if you change the reference the original value will change. PHP documentation for Passing by Reference.

php foreach key value reference

This answer seems to be favored by a lot of people on the internet, which is why I decided to add more information and words of caution. While pass by reference in foreach or functions is a clean and short solution, for many beginners this might be a dangerous pitfall.

This could be a serious problem when the variables are being reused in the same scope. Another SO question nicely illustrates why that might be a problem. As foreach relies on the internal array pointer in PHP 5, changing it within the loop may lead to unexpected behavior. The issue gets even more complicated when the array itself is a reference.

Foreach performance. In general, PHP prefers pass by value due to the copy-on-write feature. It means that internally PHP will not create duplicate data unless the copy of it needs to be changed.

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It is debatable whether pass by reference in foreach would offer a performance improvement. As it is always the case, you need to test your specific scenario and determine which option uses less memory and CPU time. For more information see the SO post linked below by NikiC. Code readability. Creating references in PHP is something that quickly gets out of hand.

If you are a novice and don't have full control of what you are doing, it is best to stay away from references. Here is more about passing by reference. How are we doing? Please help us improve Stack Overflow.

PHP foreach

Take our short survey. Learn more. PHP foreach change original array values Ask Question. Asked 8 years ago. Active 5 months ago. Viewed k times. I am very new in multi dimensional arrays, and this is bugging me big time.

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Improve this question. Ahmed Syed 1, 1 1 gold badge 16 16 silver badges 37 37 bronze badges.Join Stack Overflow to learn, share knowledge, and build your career.

Connect and share knowledge within a single location that is structured and easy to search. All I want to do is iterate over an associative array, and escape both the key and value with my sec function.

What I don't like about foreach is that I can't act on the array directly, and have to deal with creating temporary arrays and unsetting them:. This might fail if it finds something to escape in the key, adding a new element, and keeping the unescaped one. Because the language does not support this.

You'd be hard-pressed to find this ability in most languages, hence the term key. The only way to provide better alternatives is to know your specific situation. If your keys map to table column names, then the best approach is to leave the keys as is and escape them at their time of use in your SQL.

Make it a function. A function takes an input and gives an output. Your function input will be your "unsecured" array. Your output will be the result of securing the array. How are we doing? Please help us improve Stack Overflow.

Take our short survey. Learn more. Asked 9 years, 4 months ago. Active 9 years, 4 months ago. Viewed 7k times. Can someone explain to me why you can't pass a key as reference?

Would I get any performance benefit using array map than just using a foreach loop? So am I stuck with something like this? Improve this question. Ben Ben 7 7 silver badges 21 21 bronze badges.

This deserves a big old Why? Do you just overwrite the existing key? You need to explain why in your application a key could be dangerous.

Why couldn't it be dangerous? Some keys I use in mysql queries. I didn't say that they couldn't be.

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I said you need to explain why in your application a key could be dangerous. That will tell us the best approach to use for your situation. Well I modify keys and values a lot, not just for mysql. I am learning PDO, and prepared statements, slowly so it will apply less there But say I want to replace a string both in the key and value of an array, or change to uppercase, or do any number of things.

Add a comment. Active Oldest Votes.Join Stack Overflow to learn, share knowledge, and build your career. Connect and share knowledge within a single location that is structured and easy to search.

It's very confusing, but it's not even slightly idiosyncratic; it's the code executing exactly as it should. So all assignments to it are in fact assignments to the original array. What you did is easier observed in this code:. Another way is to use another variable in the second loop:. The last element of the array will remian even after the foreach loop. So its needed to use unset function outside the loop. That is. As phil stated in the comments:. Taken from the foreach manual.

See the big red box. It is recommended to destroy it by unset. To counter-act this issue, you'll have to unset the value after use, otherwise it will stay in the array as its original value if that makes sense.

You should also read this: How does PHP 'foreach' actually work? At the last iteration it gets assigned to its own value which is that of the previous iteration, so it's int 4. See also an earlier answer by me. How are we doing? Please help us improve Stack Overflow.

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Learn more. Asked 6 years, 7 months ago. Active 9 months ago. Viewed 12k times. Why is an empty foreach loop can change the result. Improve this question. Khalid Khalid 4, 5 5 gold badges 23 23 silver badges 50 50 bronze badges. The second loop seems to be causing the issue no matter what. Even if I do something useful in there, it alters the result. I'll look into it. Show 2 more comments.

Active Oldest Votes. Improve this answer. Adelmar Adelmar 1, 2 2 gold badges 16 16 silver badges 20 20 bronze badges. Isn't this a language defect? Add a comment. Alexander Gelbukh Alexander Gelbukh 1, 11 11 silver badges 27 27 bronze badges.They lie a lot how come site with 100000 visitors canot have clients to paid tipsters. They are big joke and unhonest people. They allow people to bash u if u are goodand let people to say in public that they have fixed.

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Betadvisor which is run by Albanians. Nobody earn nothing there except themthey have fake stats and best tipsters are them self.

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php foreach key value reference

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This site is run by a very friendly admin and staff. I find it on net and it is very profesional. Green Bay has won the last two meetings, both at home, by a combined 55-27 score. The Packers have held steady as three-point favorites, while the Over-Under, or total number of points Vegas thinks will be scored, stands at 50 after an open of 49.As explained in Elementary Concepts, the size of a relation between two variables, such as the one measured by a difference in means between two groups, depends to a large extent on the differentiation of values within the group.

Depending on how differentiated the values are in each group, a given "raw difference" in group means will indicate either a stronger or weaker relationship between the independent (grouping) and dependent variable. However, if the same difference of 2 was obtained from very differentiated scores (e. That is to say, reduction of the within-group variation increases the sensitivity of our test. The t-test for dependent samples helps us to take advantage of one specific type of design in which an important source of within-group variation (or so-called, error) can be easily identified and excluded from the analysis.

Specifically, if two groups of observations (that are to be compared) are based on the same sample of subjects who were tested twice (e. However, if the same sample was tested twice, then we can easily identify (or "subtract") this variation.

Specifically, instead of treating each group separately, and analyzing raw scores, we can look only at the differences between the two measures (e. By subtracting the first score from the second for each subject and then analyzing only those "pure (paired) differences," we will exclude the entire part of the variation in our data set that results from unequal base levels of individual subjects.

This is precisely what is being done in the t-test for dependent samples, and, as compared to the t-test for independent samples, it always produces "better" results (i. If these assumptions are clearly not met, then one of the nonparametric alternative tests should be used. Technically, we can apply the t-test for dependent samples to any two variables in our data set.

However, applying this test will make very little sense if the values of the two variables in the data set are not logically and methodologically comparable.

php foreach key value reference

Following, is an example of a data set that can be analyzed using the t-test for dependent samples. WCC before WCC after case 1 case 2 case 3 case 4 case 5. However, the t-test for dependent samples analysis is performed only on the paired differences"ignoring" the raw scores and their potential differentiation.

Thus, the size of this particular difference of 1 will be compared not to the differentiation of raw scores but to the differentiation of the individual difference scores, which is relatively small: 0. Compared to that variability, the difference of 1 is extremely large and can yield a highly significant t value. If there are more than two "correlated samples" (e. The repeated measures ANOVA can be considered a generalization of the t-test for dependent samples and it offers various features that increase the overall sensitivity of the analysis.

The breakdowns analysis calculates descriptive statistics and correlations for dependent variables in each of a number of groups defined by one or more grouping (independent) variables.

In the following example data set (spreadsheet), the dependent variable WCC (White Cell Count) can be broken down by 2 independent variables: Gender (values: males and females), and Height (values: tall and short). GENDER HEIGHT WCC case 1 case 2 case 3 case 4 case 5. The resulting breakdowns might look as follows (we are assuming that Gender was specified as the first independent variable, and Height as the second).

For example, in the above example, you see the means for "all males" and "all females" but you do not see the means for "all tall subjects" and "all short subjects" which would have been produced had you specified independent variable Height as the first grouping variable rather than the second.

Statistical Tests in Breakdowns. If you are interested in differences concerning the means, then the appropriate test is the breakdowns one-way ANOVA (F test). If you are interested in variation differences, then you should test for homogeneity of variances. Other Related Data Analysis Techniques.

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Although for exploratory data analysis, breakdowns can use more than one independent variable, the statistical procedures in breakdowns assume the existence of a single grouping factor (even if, in fact, the breakdown results from a combination of a number of grouping variables).

Thus, those statistics do not reveal or even take into account any possible interactions between grouping variables in the design.


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