Home > Articles > Programming > PHP

Other Array Manipulations

So far, we have only covered about half the array processing functions. Many others will be useful from time to time.

Navigating Within an Array: each, current(), reset(), end(), next(), pos(), and prev()

We mentioned previously that every array has an internal pointer that points to the current element in the array. We indirectly used this pointer earlier when using the each() function, but we can directly use and manipulate this pointer.

If we create a new array, the current pointer is initialized to point to the first element in the array. Calling current( $array_name ) returns the first element.

Calling either next() or each() advances the pointer forward one element. Calling each( $array_name ) returns the current element before advancing the pointer. The function next() behaves slightly differently—calling next( $array_name ) advances the pointer and then returns the new current element.

We have already seen that reset() returns the pointer to the first element in the array. Similarly, calling end( $array_name ) sends the pointer to the end of the array. The first and last element in the array are returned by reset() and end(), respectively.

To move through an array in reverse order, we could use end() and prev(). The prev() function is the opposite of next(). It moves the current pointer back one and then returns the new current element.

For example, the following code displays an array in reverse order:

$value = end ($array);
while ($value)
 echo "$value<br>";
 $value = prev($array);

If $array was declared like this:

$array = array(1, 2, 3);

the output would appear in a browser as


Using each(), current(), reset(), end(), next(), pos(), and prev(), you can write your own code to navigate through an array in any order.

Applying Any Function to Each Element in an Array: array_walk()

Sometimes you might want to work with or modify every element in an array in the same way. The function array_walk() allows you to do this.

The prototype of array_walk() is as follows:

int array_walk(array arr, string func, [mixed userdata])

Similar to the way we called usort() earlier, array_walk() expects you to declare a function of your own.

As you can see, array_walk() takes three parameters. The first, arr, is the array to be processed. The second, func, is the name of a user-defined function that will be applied to each element in the array. The third parameter, userdata, is optional. If you use it, it will be passed through to your function as a parameter. You'll see how this works in a minute.

A handy user-defined function might be one that displays each element with some specified formatting.

The following code displays each element on a new line by calling the user-defined function myPrint() with each element of $array:

function myPrint($value)
 echo "$value<BR>";
array_walk($array, myPrint);

The function you write needs to have a particular signature. For each element in the array, array_walk takes the key and value stored in the array, and anything you passed as userdata, and calls your function like this:

Yourfunction(value, key, userdata)

For most uses, your function will only be using the values in the array. For some, you might also need to pass a parameter to your function using the parameter userdata. Occasionally, you might be interested in the key of each element as well as the value. Your function can, as with MyPrint(), choose to ignore the key and userdata parameter.

For a slightly more complicated example, we will write a function that modifies the values in the array and requires a parameter. Note that although we are not interested in the key, we need to accept it in order to accept the third parameter.

function myMultiply(&$value, $key, $factor)
 $value *= $factor;
array_walk(&$array, "myMultiply", 3);

Here we are defining a function, myMultiply(), that will multiply each element in the array by a supplied factor. We need to use the optional third parameter to array_walk() to take a parameter to pass to our function and use it as the factor to multiply by. Because we need this parameter, we must define our function, myMultiply(), to take three parameters—an array element's value ($value), an array element's key ($key), and our parameter ($factor). We are choosing to ignore the key.

A subtle point to note is the way we pass $value. The ampersand (&) before the variable name in the definition of myMultiply() means that $value will be passed by reference. Passing by reference allows the function to alter the contents of the array.

We will address passing by reference in more detail in Chapter 5. If you are not familiar with the term, for now just note that to pass by reference, we place an ampersand before the variable name.

Counting Elements in an Array: count(), sizeof(), and array_count_values()

We used the function count() in an earlier example to count the number of elements in an array of orders. The function sizeof() has exactly the same purpose. Both these functions return the number of elements in an array passed to them. You will get a count of one for the number of elements in a normal scalar variable and 0 if you pass either an empty array or a variable that has not been set.

The array_count_values() function is more complex. If you call array_count_values($array), this function counts how many times each unique value occurs in the array $array. (This is the set cardinality of the array.) The function returns an associative array containing a frequency table. This array contains all the unique values from $array as keys. Each key has a numeric value that tells you how many times the corresponding key occurs in $array.

For example, the following code

$array = array(4, 5, 1, 2, 3, 1, 2, 1);
$ac = array_count_values($array);

creates an array called $ac that contains











3 1

This indicates that 4, 5, and 3 occurred once in $array, 1 occurred three times, and 2 occurred twice.

Converting Arrays to Scalar Variables: extract()

If we have an associative array with a number of key value pairs, we can turn them into a set of scalar variables using the function extract(). The prototype for extract() is as follows:

extract(array var_array [, int extract_type] [, string prefix] );

The purpose of extract() is to take an array and create scalar variables with the names of the keys in the array. The values of these variables are set to the values in the array.

Here is a simple example.

$array = array( "key1" => "value1", "key2" => "value2", "key3" => "value3");
echo "$key1 $key2 $key3";

This code produces the following output:

value1 value2 value3

The array had three elements with keys: key1, key2, and key3. Using extract(), we created three scalar variables, $key1, $key2, and $key3. You can see from the output that the values of $key1, $key2, and $key3 are "value1", "value2", and "value3", respectively. These values came from the original array.

There are two optional parameters to extract(): extract_type and prefix. The variable extract_type tells extract() how to handle collisions. These are cases in which a variable already exists with the same name as a key. The default response is to overwrite the existing variable. Four allowable values for extract_type are shown in Table 3.1.

Table 3.1 Allowed extract_types for extract()




Overwrites the existing variable when a collision occurs.


Skips an element when a collision occurs.


Creates a variable named $prefix_key when a collision occurs. You must supply prefix.


Prefixes all variable names with prefix. You must supply prefix.

The two most useful options are the default (EXTR_OVERWRITE) and EXTR_PREFIX_ALL. The other two options might be useful occasionally when you know that a particular collision will occur and want that key skipped or prefixed. A simple example using EXTR_PREFIX_ALL follows. You can see that the variables created are called prefix-underscore-keyname.

$array = array( "key1" => "value1", "key2" => "value2", "key3" => "value3");
extract($array, EXTR_PREFIX_ALL, "myPrefix");
echo "$myPrefix_key1 $myPrefix_key2 $myPrefix_key3";

This code will again produce the output: value1 value2 value3.

Note that for extract() to extract an element, that element's key must be a valid variable name, which means that keys starting with numbers or including spaces will be skipped.

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information

To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.


Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.


If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information

Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.


This site is not directed to children under the age of 13.


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information

If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information

Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents

California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure

Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact

Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice

We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020