php - basic introduction to arrays
TRANSCRIPT
Arrays basics
Arrays Enumeratives
vs
Arrays Associatives
Quiz - 1
$a = [ 0 => ‘A’, 1 => ‘B’, 2 => ‘C’ ];
$b = [ ‘A’ => 0, ‘B’ => 1, ‘C’ => 2 ];
a. $a is enumerative and $b is associativeb. $b is enumerative and $a is associativec. $a and $b are enumerativesd. $b and $a are associatives
Quiz - 1
$a = [ 0 => ‘A’, 1 => ‘B’, 2 => ‘C’ ];
$b = [ ‘A’ => 0, ‘B’ => 1, ‘C’ => 2 ];
a. $a is enumerative and $b is associativeb. $b is enumerative and $a is associativec. $a and $b are enumerativesd. $b and $a are associatives
Array operation
+
vs
array_merge
Quiz - 2
$a = [ 0 => ‘A’, 1 => ‘B’, 2 => ‘C’ ];
$b = [ ‘A’ => 0, ‘B’ => 1, ‘C’ => 2 ];
var_dump($a + $b);
a. [ 0 => ‘A’, 1 => ‘B’, 2 => ‘C’, 3 => ‘A’, 4 => ‘B’, 5 => ‘C’ ]b. [ ‘A’ => 0, ‘B’ => 1, ‘C’ => 2, 0 => ‘A’, 1 => ‘B’, 2 => ‘C’ ]c. [ 0 => ‘A’, 1 => ‘B’, 2 => ‘C’, ‘A’ => 0, ‘B’ => 1, ‘C’ => 2 ]
Quiz - 2
$a = [ 0 => ‘A’, 1 => ‘B’, 2 => ‘C’ ];
$b = [ ‘A’ => 0, ‘B’ => 1, ‘C’ => 2 ];
var_dump($a + $b);
a. [ 0 => ‘A’, 1 => ‘B’, 2 => ‘C’, 3 => ‘A’, 4 => ‘B’, 5 => ‘C’ ]b. [ ‘A’ => 0, ‘B’ => 1, ‘C’ => 2, 0 => ‘A’, 1 => ‘B’, 2 => ‘C’ ]c. [ 0 => ‘A’, 1 => ‘B’, 2 => ‘C’, ‘A’ => 0, ‘B’ => 1, ‘C’ => 2 ]
Quiz - 3
$a = [ 0 => 1, 1=> 2, 2 => 3 ];
$b = [ 0 => 1, 2 => NULL ];
var_dump(array_merge($a, $b));
a. [ 0 => 1, 1 => 2, 2 => 3, 3 => 1, 4 => NULL ]b. [ 0 => 1, 1=> 2, 2 => 3 ]c. [ 0 => 1, 1=> 2, 2 => NULL ]
Quiz - 3$a = [ 0 => 1, 1=> 2, 2 => 3 ];
$b = [ 0 => 1, 2 => NULL ];
var_dump(array_merge($a, $b));
a. [ 0 => 1, 1 => 2, 2 => 3, 3 => 1, 4 => NULL ]b. [ 0 => 1, 1=> 2, 2 => 3 ]c. [ 0 => 1, 1=> 2, 2 => NULL ]
With enumerative arrays the array_merge will just append in a new array every element. As a result you have a big array with all values but without the old keys.
The exception is with the associative arrays. The array merge will overwrite a value key with the last value.
Comparing arrays
==vs
===
and
!=vs!==
Quiz - 4
$a = [ 1, 2, 3 ];
$b = [ 2 => 3, 1 => 2, 0 => 1 ];
var_dump($a == $b);var_dump($a === $b);
a. true trueb. true falsec. false falsed. false true
Quiz - 4
$a = [ 1, 2, 3 ];
$b = [ 2 => 3, 1 => 2, 0 => 1 ];
var_dump($a == $b);var_dump($a === $b);
a. true trueb. true falsec. false falsed. false true
== compare just the value and key regardless the order
=== compare the value, key and order
Quiz - 5
$a = [ 1, 2, 3 ];
$b = [ 2 => 3, 1 => 2, 0 => 1 ];
var_dump($a != $b);var_dump($a !== $b);
a. true trueb. true falsec. false falsed. false true
Quiz - 5
$a = [ 1, 2, 3 ];
$b = [ 2 => 3, 1 => 2, 0 => 1 ];
var_dump($a != $b);var_dump($a !== $b);
a. true trueb. true falsec. false falsed. false true
Quiz - 6
$a = [ 1, 2, 3 ];
$b = [ ‘a’ => 1, ‘b’ => 2, ‘c’ => 3 ];
var_dump($a == $b);
a. trueb. false
Quiz - 6
$a = [ 1, 2, 3 ];
$b = [ ‘a’ => 1, ‘b’ => 2, ‘c’ => 3 ];
var_dump($a == $b);
a. trueb. false
== compare just the value and key regardless the order
Counting arrays
count
Quiz - 7
$a = [ 1, 2, 3 ];$b = [];$c = ‘Hello’;
echo count($a, COUNT_NORMAL);echo count($b, COUNT_RECURSIVE);echo count($c, COUNT_RECURSIVE);
? ? ?
Quiz - 7
$a = [ 1, 2, 3 ];$b = [];$c = ‘Hello’;
echo count($a, COUNT_NORMAL);echo count($b, COUNT_RECURSIVE);echo count($c, COUNT_RECURSIVE);
3 0 1
With count() we cannot decides when a variable is a array indeed.
Prefer to use is_array rather than count to decide when a variable is a array
Array keys
isset
vs
array_key_exists
vs
in_array
Quiz - 8
$a = [ 0 => 1, 1=> 2, 2 => 3 ];$b = [ 0 => 1, 2 => NULL ];
var_dump(isset($b[2]));var_dump(isset($a[3]));
a. true falseb. false truec. false falsed. true true
Quiz - 8
$a = [ 0 => 1, 1=> 2, 2 => 3 ];$b = [ 0 => 1, 2 => NULL ];
var_dump(isset($b[2]));var_dump(isset($a[3]));
a. true falseb. false truec. false falsed. true true
Prefer array_key_exists to determine if a key exists.
Quiz - 9
$a = [ 0 => 1, 1=> 2, 2 => 3 ];$b = [ 0 => 1, 2 => NULL ];
var_dump(array_key_exists(2, $b));var_dump(array_key_exists(3, $a));
a. true falseb. false truec. false falsed. true true
Quiz - 9
$a = [ 0 => 1, 1=> 2, 2 => 3 ];$b = [ 0 => 1, 2 => NULL ];
var_dump(array_key_exists(2, $b));var_dump(array_key_exists(3, $a));
a. true falseb. false truec. false falsed. true true
Quiz - 10
$a = [ 0 => 1, 1=> 2, 2 => 3 ];$b = [ 0 => 1, 3 => 2, 2 => NULL ];
var_dump(array_key_exists(2, $b));var_dump(isset($a[2]));
a. true falseb. false truec. false falsed. true true
Quiz - 10
$a = [ 0 => 1, 1=> 2, 2 => 3 ];$b = [ 0 => 1, 3 => 2, 2 => NULL ];
var_dump(array_key_exists(2, $b));var_dump(isset($a[2]));
a. true falseb. false truec. false falsed. true true
Quiz - 11
$a = [ 0 => 1, 1=> 2, 2 => 3 ];$b = [ 0 => 1, 3 => 2, 2 => NULL ];
var_dump(isset($b[2]));var_dump(in_array(3, $a));
a. true falseb. false truec. false falsed. true true
Quiz - 11
$a = [ 0 => 1, 1=> 2, 2 => 3 ];$b = [ 0 => 1, 3 => 2, 2 => NULL ];
var_dump(isset($b[2]));var_dump(in_array(3, $a));
a. true falseb. false truec. false falsed. true true
Quiz - 12
$a = [ 0 => 1, 1=> 2, 2 => 3 ];$b = [ 0 => 1, 3 => 2, 2 => NULL ];
var_dump(isset($b[2]));var_dump(in_array(3, $a));var_dump(in_array(NULL, $a))
a. true false trueb. false true falsec. false false falsed. true true true
Quiz - 12
$a = [ 0 => 1, 1=> 2, 2 => 3 ];$b = [ 0 => 1, 3 => 2, 2 => NULL ];
var_dump(isset($b[2]));var_dump(in_array(3, $a));var_dump(in_array(NULL, $a))
a. true false trueb. false true falsec. false false falsed. true true true
