Method summary analysis based on PHP traversal group

1. foreach()
foreach() is one of the simplest and most efficient ways to iterate over data in groups.
#example1:

<?php
$colors= array('red','blue','green','yellow');
foreach ($colorsas$color){
echo "Do you like $color? <br />";
}
?>

Display results:
Do you like red?
Do you like blue?
Do you like green?
Do you like yellow?

2. while()
while() is usually used in conjunction with list() and each().
#example2:

<?php
$colors= array('red','blue','green','yellow');
while(list($key,$val)= each($colors)) {
echo "Other list of $val.<br />";
}
?>

Display results:
Other list of red.
Other list of blue.
Other list of green.
Other list of yellow.

3. for()
#example3:

<?php
$arr= array ("0"=> "zero","1"=> "one","2"=> "two");
for ($i= 0;$i< count($arr); $i++){
$str= $arr[$i];
echo "the number is $str.<br />";
}
?>

Display results:
the number is zero.
the number is one.
the number is two.

========== =
key()
mixed key(array input_array)
The key() function returns the key element in input_array at the current pointer position.
#example4

<?php
$capitals= array("Ohio"=> "Columbus","Towa"=> "Des Moines","Arizona"=> "Phoenix");
echo "<p>Can you name the capitals of these states?</p>";
while($key= key($capitals)) {
echo $key."<br />";
next($capitals);
// each key() The call does not advance the pointer. To do that next() function 
}
?>

Display results:
Can you name the capitals of these states?
Ohio
Towa
Arizona
reset()
mixed reset(array input_array)
The reset() function is used to set the pointer to input_array back to the beginning of the array. This function is often used if you need to view or process the same array more than once in a script, and it is also often used at the end of sorting.
#example5 - Appends code to #example1

<?php
$colors= array('red','blue','green','yellow');
foreach ($colorsas$color){
echo "Do you like $color? <br />";
}
reset($colors);
while(list($key,$val)= each($colors)) {
echo "$key=> $val<br />";
}
?>

Display results:
Do you like red?
Do you like blue?
Do you like green?
Do you like yellow?
0 = > red
1 = > blue
2 = > green
3 = > yellow
Note: Assigning one array to another resets the pointer to the original array, so in the above example, assigning $colors to another variable inside the loop will result in an infinite loop.
For example, $s1 = $colors; Add to the while loop, execute the code again, and the browser will display the results endlessly.
each()
array each(array input_array)
The each() function returns the current key/value pair of the input array and pushes the pointer one position. The returned array contains four keys, keys 0 and key contain the key name, and keys 1 and value contain the corresponding data. If the pointer before each() is at the end of the array, FALSE is returned.
#example6

<?php
$capitals= array("Ohio"=> "Columbus","Towa"=> "Des Moines","Arizona"=> "Phoenix");
$s1= each($capitals);
print_r($s1);
?>

Display results:
Array ( [1] = > Columbus [value] = > Columbus [0] = > Ohio [key] = > Ohio )
current(), next(), prev(), end()
mixed current(array target_array)
The current() function returns the array value at the current pointer position of the target_array array. Unlike the next(), prev(), and end() functions, current() does not move the pointer.
The next() function returns the array value placed next to the current array pointer.
The prev() function returns the value of the array at the first position of the current pointer, or FALSE if the pointer is already at the first position of the array.
The end() function moves the pointer to the last position of target_array and returns the last element.
#example7

<?php
$fruits= array("apple","orange","banana");
$fruit= current($fruits); //return "apple"
echo $fruit."<br />";
$fruit= next($fruits); //return "orange"
echo $fruit."<br />";
$fruit= prev($fruits); //return "apple"
echo $fruit."<br />";
$fruit= end($fruits); //return "banana"
echo $fruit."<br />";
?>

Display results:
apple
orange
apple
banana
======== test the speed of 3 kinds of traversal groups ========
Generally, there are three ways to traverse an array, for, while, and foreach. The simplest and most convenient is foreach. Let's first test the time it takes to walk through a 1 dimensional array with 50000 subscripts.
Test environment:
Intel Core Due2 2GHz
2GB 1067MHz DDR3
Mac OS X 10.5.7
Apache 2.0.59
MySQL 5.0.41
PHP 5.2.6
#example8

<?php
$arr= array();
for($i= 0; $i< 50000; $i++){
$arr[]= $i*rand(1000,9999);
}
function GetRunTime()
{
list($usec,$sec)=explode(" ",microtime());
return ((float)$usec+(float)$sec);
}
######################################
$time_start= GetRunTime();
for($i= 0; $i< count($arr); $i++){
$str= $arr[$i];
}
$time_end= GetRunTime();
$time_used= $time_end- $time_start;
echo 'Used time of for:'.round($time_used, 7).'(s)<br /><br />';
unset($str, $time_start, $time_end, $time_used);
######################################
$time_start= GetRunTime();
while(list($key, $val)= each($arr)){
$str= $val;
}
$time_end= GetRunTime();
$time_used= $time_end- $time_start;
echo 'Used time of while:'.round($time_used, 7).'(s)<br /><br />';
unset($str, $key, $val, $time_start, $time_end, $time_used);
######################################
$time_start= GetRunTime();
foreach($arr as$key=> $val){
$str= $val;
}
$time_end= GetRunTime();
$time_used= $time_end- $time_start;
echo 'Used time of foreach:'.round($time_used, 7).'(s)<br /><br />';
?>

Test results:
Used time of for:0.0228429(s)
Used time of while:0.0544658(s)
Used time of foreach:0.0085628(s)
After repeated tests, the results show that foreach is the fastest and the slowest to traverse the same array. In principle, foreach operates on a copy of the array (by copying the array), while while operates by moving the internal index of the array. In general logic, while should be faster than foreach (because foreach first copies the array when it executes, and while moves the internal index directly). But the opposite is true. The reason should be that foreach is the internal implementation of PHP and while is the general circulation structure. Therefore, foreach is simple and efficient in common applications. Under PHP5, foreach can also traverse the attributes of a class.