Converting text file into multi-dimensional associative array in PHP

Question

I have this lab problem that I've now been stuck on for three days and I'm pretty sure after countless googling and trying pretty much everything I can find, that I've just confused myself to the point of being utterly lost. I'm not sure if this is what you guys do, but essentially I want the answer with a "how to" of how you got there. In my head I know what I want to do but just cannot fathom getting this into code.

To start, I have a text file, postcode.txt, with a list of postcodes and their respective suburbs like so:

3000,MELBOURNE
3001,MELBOURNE
3002,EAST MELBOURNE
3003,WEST MELBOURNE

This needs to be put into an array with the suburb names as the keys, and the postcodes as the values. As you can see, some suburbs have more than one postcode. Am I correct in thinking this will be a multi-dimensional associative array?

I'm not sure if it's best to use file() or file_get_contents() as I'm very new to PHP and have never even used an array before, let alone something this confusing. I can then assume I need to explode the lines of text by ',' and somehow have the suburbs as keys and the postcodes as values.

Once this is in an array I need to search this array by way of user input for a particular suburb name and it needs to return the value or values of that suburb. From the things that I have tried it isn't returning values at all so I can only assume it's something to do with case sensitivity or white spaces etc.

I'm not entirely sure why this is a lab question when I've yet to have any lab questions dealing with simple arrays, but nothing I can do except desperately try and understand this. It's been driving me mad. Any help is very much appreciated.

Answer 1

Reading your file

To start with, opening the file... file() is the easiest method to read a file into an array as it is performed with one line.

Drawbacks:

• file() can be slow for larger files, as it needs to read the entire file into an array before you can use it

Alternatively, use the standard file open structure using something like fgets() to read it line by line.

Drawbacks:

• more lines of code required

Let's use file() as an example:

$lines = file('postcodes.txt');

---

Getting the array structure

The first part of your question is how to get the array structure you want, which is the suburb name as the array key and all the post codes as the values. There are plenty of ways to do this - here's a simple example using a foreach:

// Define an empty array to start with
$postcodes = array();
// Loop each line
foreach($lines as $line) {
    // Split the line by the comma and define the variables with each part
    // mapping trim to the array to remove any whitespace on either end
    list($postcode, $suburb) = array_map('trim', explode(',', $line));
    // Check the array key exists in post codes
    if(!array_key_exists($suburb, $postcodes)) {
        // If not, define it to start with
        $postcodes[$suburb] = array();
    }

    // Check if the postcode is already in the array
    if(in_array($postcode, $postcodes[$suburb])) {
        // Skip this postcode, it's already where it should be
        continue;
    }

    // Add the postcode to it
    $postcodes[$suburb][] = $postcode;
}

Docs: array_map(), array_key_exists(), in_array(), explode(), foreach, continue

An output of the resulting array would yield something like this:

Array
(
    [MELBOURNE] => Array
        (
            [0] => 3000
            [1] => 3001
        )

    [EAST MELBOURNE] => Array
        (
            [0] => 3002
        )

    [WEST MELBOURNE] => Array
        (
            [0] => 3003
        )

)

---

Searching the array

Searching is a kettle of fish, and there are many things to consider. Do you want to return a case sensitive result, case insensitive, partial results, multiple results etc?

Here are some options and what you should use for them:

• Exact match (single): array_keys($postcodes, 'suburb name')
• Exact match (multiple): wouldn't happen as you're using array keys (unique by definition)
• Partial match (single): a loop, strstr() (case sensitive) or stristr() (case insensitive) matching the key and the search term and killing the loop if it is found
• Partial match (multiple): same as above, but don't kill the loop if it's found, instead add to an array of matched results and return that

Here's an example function to return all partially matches results from the array:

function search($postcodes, $search_term) {
    // Define empty array for matches
    $matches = array();
    // Trim the search string to remove whitespace from either end
    $search_term = trim($search_term);
    // Loop through postcodes
    foreach($postcodes as $suburb => $post_codes) {
        // Case insensitive comparison
        if(stristr($suburb, $search_term)) {
            // It matches! Add entire result to return array
            $matches[$suburb] = $post_codes;
        }
    }
    // Return result
    return $matches; 
}

Example use:

print_r($search($postcodes, 'melbourne'));
print_r($search($postcodes, 'east'));

Array
(
    [MELBOURNE] => Array
        (
            [0] => 3000
            [1] => 3001
        )

    [EAST MELBOURNE] => Array
        (
            [0] => 3002
        )

    [WEST MELBOURNE] => Array
        (
            [0] => 3003
        )

)
Array
(
    [EAST MELBOURNE] => Array
        (
            [0] => 3002
        )

)

Looking forward, you might also want to match any of the search terms passed in as a string, e.g. "east west" to match both east and west Melbourne. In this case you'll need to explode the search string to spaces, and perform a search on each term. You'll need to ensure to only return unique values here. Here's an example of a function that would do that:

function search_multi($postcodes, $search_term) {
    // Define empty array for matches
    $matches = array();
    // Trim the search string
    $search_term = trim($search_term);
    // Get all search terms
    $search_terms = explode(' ', $search_term);
    // Loop through search terms
    foreach($search_terms as $term) {
        // Loop through postcodes
        foreach($postcodes as $suburb => $post_codes) {
            // First, check that this result hasn't already been found! (unique)
            if(array_key_exists($suburb, $matches)) {
                // It's already been found, skip this one...
                continue;
            }
            // Case insensitive comparison
            if(stristr($suburb, $term)) {
                // It matches! Add entire result to return array
                $matches[$suburb] = $post_codes;
            }
        }    
    }
    // Return result
    return $matches; 
}

And given you search for "east west", the result would be:

Array
(
    [EAST MELBOURNE] => Array
        (
            [0] => 3002
        )

    [WEST MELBOURNE] => Array
        (
            [0] => 3003
        )

)

---

Conclusion

This kind of data structure would be best to be stored in a database if it's going to be used more than once, but to parse a text/CSV file this is how you'd approach it. Hope this helps.