CS 85  PHP Programming

Arrays

Reference: Programming PHP by Rasmus Lerdorf

Examples: Chapter 5  Arrays

• array - a collection of data values, organized as an ordered collection of key-value pairs
• very common and useful
• examples:
  • a set of email addresses
  • items from a select element that permits multiple selections

Indexed Versus Associative Arrays

• two kinds of arrays in PHP
  1. indexed
     • keys are integers; 0-based
  2. associative
     • keys are strings
     • like two-column table: first column is key, second column is value
• internally, all arrays are associative
• keys are unique
• arrays have an internal order
  • there are functions to traverse array in this order
  • order is normally that in which values were inserted
  • can change order with sorting functions

Identifying Elements of an Array

• access values with arrayName[key]
• key aka index
• e.g., $names[0], $names['0'], $age['Jack']
• if the index is a constant, its value is used
• don't quote the key of an interpolated array lookup; e.g., "Hello, $person[name]";

Storing Data in Arrays

• storing a value in an array will create the array if necessary
• can initialize an array with the array() construct
  • builds array from args
  • array(val1, ...)
  • array(key1 => val1, ...)
  • array() // builds an empty array

Adding Values to the End of an Array

• use [] syntax
• e.g., $family[] = 'Pawel';

Assigning a Range of Values

• range(lb, ub)
• creates an array of consecutive integers or character values
• e.g., range(1, 100)
• e.g., range('a', 'z')
• e.g., range('able', 'zooey') same as range('a', 'z')

Getting the Size of an Array

• count(arrayName)
• alias sizeof(arrayName)
• return number of elements in the array

Padding an Array

• to create an array initialized to the same value
• newArray = array_pad(existingArray, minimumElements, value)
• use negative value for minimumElements to add to the start of the array

Multidimensional Arrays

• array values can be arrays
• refer to elements with more []s
• to interpolate an array lookup in a multidimensional array, enclose in {}; e.g., "the name is {$name[0][1]}."

Extracting Multiple Values

• to copy all array values into variables
• list(varList) = arrayName;
• construct (not a function)
• copied in internal order
• extra values in arrayName are ignored
• extra values in varList are set to NULL

Slicing an Array

• array arr2 = array_slice(array arr1, int offset, int length);
• arr2 will have numeric keys starting at 0
• combine with list()  to extract only some values to variables

Splitting an Array into Chunks

• divides array into smaller, evenly sized arrays
• array chunks array_chunk(array arr, int size, [, bool preserve_keys])

Keys and Values

• array keys array_keys(array arr)
• returns keys in internal order

Checking Whether an Element Exists

• array_key_exists(key, array)
• similar to isset(), but not quite the same

Removing and Inserting Elements in an Array

• array_splice(array arr, int start, [, int length [, array replacement]]

Converting Between Arrays and Variables

Creating Variables from an Array

• extract(array arr [, int extract_type] [, string prefix])
• the keys become the variable names
• if the variable name already exists, it is overwritten

Creating an Array from Variables

• array arr compact('var1', 'var2', ...)
• array arr compact(array arr)
• creates an associative array with keys 'var1', 'var2', ...

Traversing Arrays

• typically we need to process each element of an array

The foreach Construct

• most common way to loop over an array's elements
• see ch. 2
• operates on a copy of the array

The Iterator Functions

• iterator - the pointer to the current element (of the array)
• current() - returns the current element
• reset() - moves iterator to first element; returns the element
• next() - moves iterator to next element; returns the element
• prev() - moves iterator to previous element; returns the element
• end() - moves iterator to last element; returns the element
• each() - returns the key and value of the current element (as an array); moves iterator to next element
• key() - returns the key of the current element
• Example 5-1web.php  Building a table with the iterator functions

Using a for Loop

• for indexed arrays
• operates on the array itself
• processes elements in key order (regardless of internal order)

Calling a Function for Each Array Element

• array_walk(array arr, string function_name, arg)
• function_name has two or three parameters - element value, key, thirdArgumentToArray_walk
• processes elements in their interal order

Reducing an Array

• mixed result array_reduce(array arr, string function_name [, default])
• applies a function to each element
• builds a single value

Searching for Values

• bool found in_array(mixed to_find, array arr [, bool strict])
  • strict == true requires type to match
  • Example 5-2-b.php  Searching an array
• mixed key array_search(mixed to_find, array arr [, bool strict])
  • returns key of found element

Sorting

• changes the internal order of the elements

Sorting One Array at a Time

• nine sort functions
  1. sort() - standard
  2. rsort() - reverse
  3. usort() - user
  4. asort() - associative
  5. arsort() - associative reverse
  6. uasort() - user associative
  7. ksort() - key
  8. krsort() - key reverse
  9. uksort() - user key
• Example 5-3-b.php  Sorting arrays

Natural-Order Sorting

• natsort() - natural
• natcasesort() - natural lowercase

Sorting Multiple Arrays at Once

• array_multisort(array arr1 [, int sort_order] [, array arr2 [, int sort_order] ...)
• similar to a join operation on a database

Reversing Arrays

• array arr2 = array_reverse(array arr1)
  • reverses the internal order of the elements
• array arr2 array_flip(array arr1)
  • switches keys with values

Randomizing Order

• shuffle(array arr)
• puts elements in random order

Acting on Entire Arrays

Calculating the Sum of an Array

• mixed sum array_sum(array arr)

Merging Two Arrays

• array result array_merge(array arr1, array arr2, ...)

Calculating the Difference Between Two Arrays

• see later section on sets

Filtering Elements from an Array

• array result array_filter(array arr1, string function_name)
• result is an array containing the elements of arr1 for which function_name returns true

Using Arrays

• arrays appear in almost all PHP programs
• can use arrays to implement sets, stacks, and queues

Sets

• basic operations: union, intersection, difference
• can use arrays, but must remove duplicates
• union
  • all elements from both sets
  • array_unique(array_merge(array1, array2, ...));
• intersection
  • elements common to all sets
  • array_intersect(array1, array2, ...)
• difference
  • elements in array1 that are not in array2
  • array_diff(array1, array2)

Stacks

• LIFO data structure
• array_push($array, value)
  • same as assignment to $array[]
• array_pop($array)
  • removes last element from $array
  • returns the element
• useful for maintaining state
• Example 5-4web.php  State debugger

Queues

• array_shift()
• array_unshift()

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