Array Exercises (PHP)

Array Exercises (PHP).markdown

Array Exercises (PHP)

Questions

1. If you have an array $a = array( 0, 1, 2, 3, 4 );, how do you extract the value 3 from the array?

2. If you have an array $a = array( "zero"=>0, "one"=>1, "two"=>2, "three"=>3, "four"=>4 );, how do you extract the value 3 from the array?

3. If you have the following array, how do you extract the value 3 from the array?

   $a = array(
       array(
           0,
           1
       ),
       array(
           2,
           array(
               3
           )
       )
   );
   

4. If you have the following array, how do you extract the value 3 from the array?

   $a = array(
       "a"=>array(
           "b"=>0,
           "c=>1
       ),
       "b"=>array(
           "e"=>2,
           "o"=>array(
               "b"=>3
           )
       )
   );
   

5. Create a new array with each comma-separated value as its own array element from the string $a = "a,b,c,d,e,f".

6. With the result array from 5, create a new array where each element is both key and value. In other words, the result should be:

   array(
       "a"=>"a",
       "b"=>"b",
       "c"=>"c",
       "d"=>"d",
       "e"=>"e"
   )
   

7. You have two arrays like the following. One contains field labels, the other contains field values. Write a program to output the third array.

   $keys = array(
       "field1"=>"first",
       "field2"=>"second",
       "field3"=>"third"
   );
   $values = array(
       "field1value"=>"dinosaur",
       "field2value"=>"pig",
       "field3value"=>"platypus"
   );
   // want to output
   $keysAndValues = array(
       "first"=>"dinosaur",
       "second"=>"pig",
       "third"=>"platypus"
   );
   

8. You have an array of transactions, each of which has a debit and credit amount. Find the absolute value of the transaction amount (i.e. abs( debit - credit )) and add it as a new key=>value pair to each transaction.

   $transactions = array(
       array(
           "debit"=>2,
           "credit"=>3
       ),
       array(
           "debit"=>15,
           "credit"=>14
       )
   );
   // outputs
   $transactions = array(
       array(
           "debit"=>2,
           "credit"=>3,
           "amount"=>1
       ),
       array(
           "debit"=>15,
           "credit"=>14,
           "amount"=>1
       )
   );
   

9. Find the sum of this array of numbers $a = array( 0, 1, 2, 3, 4, 5, 6 );.

Sample Answers (others may be correct :-D)

1. $a[ 3 ];

2. $a[ "three" ];

3. $a[ 1 ][ 1 ][ 0 ];

4. $a[ "b" ][ "o" ][ "b" ];

5. $a = explode( ",", $a );

6. Samples:

   $new_array = array();
   foreach( $a as $element ) {
       $new_array[ $element ] = $element;
   }
   

   or

   array_combine( $a, $a );

   How would you write your own array_combine function?

7. Samples:

   // can you spot the bug?
   $keysAndValues = array();
   $keysAndValues[ $keys[ "field1" ] ] = $values[ "field1value" ];
   $keysAndValues[ $keys[ "field2" ] ] = $values[ "field2value" ];
   $keysAndValues[ $keys[ "field3" ] ] = $values[ "field2value" ];
   

   or

   $keysAndValues = array();
   foreach( array( 1, 2, 3 ) as $index ) {
       $keysAndValues[ $keys[ "field$index" ] ] = $values[ "field" . $index . "value" ];
   }
   

   or

   $keysAndValues = array_combine( array_values( $keys ), array_values( $values ) );
   

8. Samples

   $new_transactions = array();
   foreach( $transactions as $transaction ) {
       $new_transaction = $transaction;
       $new_transaction[ "amount" ] = abs( $transaction[ "debit" ] - $transaction[ "credit" ] );
       $new_transactions[] = $new_transaction;
   }
   $transactions = $new_transactions;
   

   or

   $transactions = array_map( function( $transaction ) {
       $transaction[ "amount" ] = abs( $transaction[ "debit" ] - $transaction[ "credit" ] );
       return $transaction;
   }, $transactions );
   

9. Samples:

   $sum = 0;
   foreach( $a as $element ) {
       $sum += $element;
   }
   

   or

   $sum = array_reduce( $a, function( $partial_sum, $element ) {
       return $partial_sum + $element;
   }, 0 );
   

   or

   $sum = array_sum( $a );
   

Fixed = that should have been - in sample answers for #8. Thanks, @sajinshrestha!

where are the answers?

where are the answers?

@Boogyman63 The answers should be right inline, starting at Sample Answers. As noted, there are definitely lots of ways to solve most of these questions.

1. If you have an array $a = array( 0, 1, 2, 3, 4 );, how do you extract the value 3 from the array?

2. If you have an array $a = array( "zero"=>0, "one"=>1, "two"=>2, "three"=>3, "four"=>4 );, how do you extract the value 3 from the array?
   <?php
   //Creating an associative array
   $a =array("zero" => "0", "one" => "1", "two" => "2", "three" => "3", "four"=>4);
   echo $a["three"];

    ?>
   

3. If you have the following array, how do you extract the value 3 from the array?

4. If you have the following array, how do you extract the value 3 from the array?

array( "b"=>0, "c"=>1 //Fixed the typo here, changed "c=>1" to "c"=>1 ), "b"=>array( "e"=>2, "o"=>array( "b"=>3 ) ) ); echo $a["b"]["o"]["b"]; ?>

5. Create a new array with each comma-separated value as its own array element from the string $a = "a,b,c,d,e,f".