PHP Array

Posted 2021-03-14 Coding_Changes_LIfe

            <?php
//1.initiate an array
            //1
            $a = array(1, 2, 3);
            //2
            $b = [4, 5, 6];
            //3
            $numbers = range(1, 10); //1,2,3,4,5,6,7,8,9,10
            $odds = range(1, 10, 2); //1,3,5,7,9
            $odds = range(10, 1, -1); //9,7,5,3,1
            $letters = range('a', 'z'); //a-z
            echo '<pre>';
            //var_dump($numbers);
            //var_dump($odds);
            //var_dump($letters);
            $a[3] = 4;  //automatically resize the array
            //4
            $student = ['amy', 'joseph', 'mike'];
            //read array
            for ($i = 0; $i < 3; $i++) {
                // echo $student[$i];
            }
            
            foreach ($student as $name) {
                //echo $name.'foreach';
            }
            //5
            $grades = array('amy' => 89, 'joseph' => 99, 'mike' => 100);
            //6
            $grades = array('amy' => 89);
            $grades['joseph'] = 99;
            $grades['mike'] = 100;
            //7
            $grades['amy'] = 89;
            $grades['joseph'] = 99;
            $grades['mike'] = 100;
            
//2.using loops
            foreach ($grades as $student => $grade) {
                //echo $student.'='.$grade;
            }
            while ($element = each($grades)) {
                //var_dump($element);
            }
            reset($grades); //because each() tracks every elements to next one, if you want to use the array again you need to reset it
            while (list($stu, $grade) = each($grades)) {
                //echo $stu.'='.$grade;
            }
            
//3.sort
            $student = ['zamy', 'joseph', 'mike'];
            
            sort($student);//sort by ASCII
            //print_r($student);
            $file = array(file01, file06, file02);
            sort($file, SORT_NATURAL);//sort by ASCII
            //print_r($file);
            
            $product = array('oil' => 100, 'tyre' => 58, 'plugs' => 45);
            asort($product);//sort by value
            //print_r($product);
            ksort($product);  //sort by key
            //print_r($product);
            //ascending above  descending corespondingly are rsort(), arsort(), krsort();
            
            $products = array(
                array('eTLR', 'aTires', 100), //code, desc, price,x
                array('gOIL', 'bOil', 10),
                array('fSPK', 'cSpark Plugs', 4)
            );
            ///for multi-mension array
            array_multisort($products);  //sort by the first element
            //print_r($product);
            
//4.usort  user-defined sort
            function compare($x, $y)
            { // x is a kind of product
                if ($x[0] == $y[0]) {  //0 stands for eTLR,,,, 1 stands for aTires, 2 stands for 100
                    return 0;
                } elseif ($x[0] > $y[0]) {  //x > y return 1 then ascending, vice versas, if x<y, return 1, descending
                    return 1;
                } else {
                    return -1;
                }
            }
            
            usort($products, 'compare'); //compare is a "callable" ,also change the array, this function is from multi-mension arrays
            //similarly there also other functions such as:  uasort(), uksort(),
            print_r($products);
            shuffle($product);
            $reversedArray = array_reverse($product);   // there is no &, so this function does not change the product array, instead it returns a reverse array
            
            $numbers = array();
            for ($i = 10; $i > 0; $i--) {
                array_push($numbers, $i); // add the end element of the nmubers
            }
            //print_r($numbers);
            array_pop($numbers); //remove the end element from the numbers
            //print_r($numbers);
            $str = '123d3ll3';
            echo intval($str); //123
            
//5.array pointer ： every array has a internal pointer that pointed the current element
            $arr = array(1, 2, 3, 4, 5);
            echo current($arr);  //1
            echo each($arr); //return array(1=>2)  but pointer points to the next one 2
            echo next($arr); // 3
            echo end($arr); //5
            echo prev($arr); //4
            echo '<br/>';
            
 //6. array_walk($arr,callable func[, mixed userData])          
            //applying any function to each element in a array. using array_walk($arr,callable func[, mixed userData]) callable func is the  name of a user-defined function that applies the same change to every element.
            function myPrint($value)
            {
                echo "$value<br/>";
            }
            
            //this will not change the arr due to &,using  for loop
            array_walk($arr, "myPrint");  //myPrint is the name of the function,
            print_r($arr);
            echo "<hr>";
            //function myMultiply($v, $key, $factor){ //there is a sequence of $value and $key, the first one is the value and second is the key. $key is not used although declared here
            //   $v *= $factor;
            //    echo "$v<br/>";
            //}
            
            //this will not change the arr due to & in the first parameter
            function myMultiply(&$v, $k, $factor)
            { //&$v means that $v will be passed by reference
                $v *= $factor;
                echo "$v<br/>";
            }
            
            array_walk($arr, "myMultiply", 5);  //
            print_r($arr);
            
            echo count($arr); //5
            echo sizeof($arr); //5
            
 //7.array_count_values();
            //caculate the frequency of the element in a array
            $arrF = array(1, 3, 4, 3, 3, 2, 4, 2, 1);
            $ac = array_count_values($arrF);
            print_r($ac); //k => v, 1 =>2  means 1 digit occurs 2 times in the arrF``````````````1
            echo "<hr>";
            
 //8.extract();
            $array = array('key1' => 'value1', 'key2' => 'value2', 'key3' => 'value3');
            extract($array);
            echo $key1, $key2, $key3;  //value1value2value3
            
            //$key1,$key2,$key3 variables already exist
            $arr2 = array('key1' => 'valueA', 'keyB' => 'valueB', 'keyC' => 'valueC');
            extract($arr2);
            //extract($arr2),EXTR_OVERWRITE); by default
            echo $key1, $keyB, $keyC; //valueAvalueBvalueC
            
            extract($array, EXTR_PREFIX_ALL, 'myPrefix');  //link variable with _
            echo $myPrefix_key1, $myPrefix_key2, $myPrefix_key3; //value1value2value3