PHP Arrays Ex. #5: Associative Array

In this PHP exercise, you will again use the list of cities in Arrays Exercise #2. Here's the list, this time including countries as well as cities:

Tokyo, Japan; Mexico City, Mexico; New York City, USA; Mumbai, India; Seoul, Korea; Shanghai, China; Lagos, Nigeria; Buenos Aires, Argentina; Cairo, Egypt; London, England.

This time, create an associative array, using the countries as keys, the cities as values. Create a form for the user, with the instructions Please choose a city:

Follow this request with a select field for the 10 cities, with the options created by looping through the array. When the user clicks the submit button, return the statement $city is in $country., where $city is the value chosen by the user, and $country is its key.

Here's the code:

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"

     "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

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<html xmlns="http://www.w3.org/1999/xhtml"  xml:lang="en" lang="en">

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<head>
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<meta http-equiv="content-type" content="text/html;charset=iso-8859-1" />

<title>Associative Array - Cities</title>

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</head>
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<body>
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<h2>Large Cities Again<br /></h2>
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<?php
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  //Create associative array with countries as keys, cities as values.

```
  $cities=array(
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    "Japan" => "Tokyo",
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    "Mexico" => "Mexico City",
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    "USA" => "New York City",
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    "India" => "Mumbai",
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    "Korea" => "Seoul",
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    "China" => "Shanghai",
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    "Nigeria" => "Lagos",
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    "Argentina" => "Buenos Aires",
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    "Egypt" => "Cairo",
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    "UK" => "London"
```
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  );
```

  //If form not submitted, display form.

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  if(!isset($_POST['submit'])){
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?>
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<form method="post" action="yourfile.php">

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<p>Please choose a city:</p>
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<select name="city">
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<?php
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  //Use array to create options for select field.

  //Be sure to escape the quotes and include a line feed.

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  foreach($cities as $c){
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    echo "<option value=\"$c\">$c</option>\n";

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  }
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?>
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</select> <p />
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<input type="submit" name="submit" value="Go">

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</form>
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<?php
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  //If form submitted, process input.
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  }else{
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    //Retrieve user response.
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    $city=$_POST['city'];
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    //Find corresponding key in associative array.

    $country=array_search($city, $cities);

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    //Send the data back to the user.
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    echo "<p>$city is in $country.</p>" ;

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  }
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?>
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</body>
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</html>
```

See the output of the script in a separate window here. You can also view the output's HTML source from the new window, if you need to check that.

Comments

Really like your website.

Permalink Submitted by MISTEROUIJA on Mon, 03/11/2013 - 09:57.

I Really like your website. It's nice to have exercises to do to test what you've learnt.

Here is my solution.


<h2>Associative Array</h2>
<?php

//create associative array
$cities = array(
	'Japan'=>'Tokyo',
	'Mexico'=>'Mexico City',
	'USA'=>'New York City', 
	'India'=>'Mumbai',
	'Korea'=>'Seoul',
	'China'=>'Shanghai',
	'Nigeria'=>'Lagos', 
	'Argentina'=>'Buenos Aires', 
	'Egypt'=>'Cairo', 
	'England'=>'London' 
	);
	if(!isset($_POST['submit'])){	
?>

<form method="post" action="arraystwo.php">
	<p>
	Please choose a city:
	<select name="city" size="1" >
		<?php
		//loop through array to create options
		foreach($cities as $x){
		echo "$x";
		}
		?>
	</select>
	</p>
	<p><input type="submit" name="submit" value="Send" /></p>
</form>
<?php
}
else{
//Get user selection
$city = $_POST['city'];
//Flip array so the keys become the value
$country = array_flip($cities);

echo "<p>$city is in $country[$city]</p>";

}
?>

I really like your solution

Permalink Submitted by Bladeoz on Mon, 08/05/2013 - 01:22.

I was stuck with attempting to pull out the key from the array. I tried several different functions to no avail, but your idea of flipping the array is brilliant.

Thank you a million!

(FYI: I attempted to create a function that could be reused to display the form, and ask users to type in the city name to get the Country they required, just for fun). Not sure I should post consider it's off on a tangent.

array_search not returning any data

Permalink Submitted by vanquish12 on Fri, 07/12/2013 - 04:03.

I can only get array_search to return the key when I put in the literal text of the value field, e.g. London. It will not work if I substitute the $_POST variable, or the variable that I assign to the $_Post variable. My code is below, if you can help! Thank you.

```
 <?php
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$places = array(
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	"Japan" => "Tokyo",
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    "Mexico" => "Mexico City",
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    "USA" => "New York City",
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    "India" => "Mumbai",
```
```
    "Korea" => "Seoul",
```
```
    "China" => "Shanghai",
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```
    "Nigeria" => "Lagos",
```
```
    "Argentina" => "Buenos Aires",
```
```
    "Egypt" => "Cairo",
```
```
    "UK" => "London");
```
```
 
```
```
 
```
```
?>
```
```
 
```
```
Please pick a city:
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```
<form action="" method="post">
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	<select name="city">
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<?php
```
```
	foreach ($places as $key => $value) {
```

?>	<option value=" <?php echo $value ; ?>"><?php echo $value;

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}?>
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	</select>
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	<input type="submit">
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</form>
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<?php
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if(isset($_POST['city'])) {
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```
		$ciudad = $_POST['city'];
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		$country = array_search($_POST['city'], $places);

		echo "You have chosen" . $_POST['city'] . ", which is in" . $country;

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} else {
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	echo "no";
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}
```

multiple selection capable

Permalink Submitted by Joe Play on Sat, 09/28/2013 - 06:35.

Here is my take for this exercise. You can select multiple entries, and all corresponding results will be displayed. It is short and simple.

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<html>
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<head><title>Select Field Exercise - Joe Play</title></head>

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<body>
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```
	<?php		
```

		$places=array('Japan'=>'Tokyo','Mexico'=>'Mexico City','USA'=>'New York City','India'=>'Mumbai',

		'South Korea'=>'Seoul','China'=>'Shanghai','Nigeria'=>'Lagos','Argentina'=>'Buenos Aires',

		'Egypt'=>'Cairo','England'=>'London');

```
 
```

		if (!empty($_POST["selectedPlace"])) {

			foreach($_POST["selectedPlace"] as $selectedCity){

				foreach($places as $country => $city)

					if($city==$selectedCity) echo"$city is in $country.<br/>";

```
			}
```
```
		}		
```

		echo"<br/>Please choose a city: <br/>(Press and hold CTRL key for multiple selection)<br/>";

```
		echo"<form action='' method='post'>";
```

			echo"<select name='selectedPlace[]' multiple='yes' size='".count($places)."'>";

				foreach($places as $country => $city){

					echo"<option value=\"$city\">$city</option>";

```
				}
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```
			echo"</select>";
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			echo"<br/><input type='submit' value='Check it!' />";

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		echo "</form>";
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	?>							
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</body>
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</html>
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