up vote 2 down vote favorite

I'm not familiar with PHP associate arrays so I'm hoping someone can shed some light on the subject and suggest how to solve my particular problem.

I have an array of data, of which each element is a string of "Month, Year". I want to parse through that data and create an associate array where the keys are the years and the values are an array of months of that year.

For example, I have the array("November, 2011", "May, 2011", "July, 2010") Using a foreach loop, I want to parse through this data and create the array:

array( "2011" => array("Novemeber", "May"), "2010" => array("July"))

From what I can see, I need to know how to check if a key is there, if it isn't create it and make a new array as its value, if it is, append the month to the already there value array.

If that makes sense, any help would be appreciated! thanks!

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"associative" arrays, just to be nit-picky. – Marc B Nov 18 '11 at 21:39

4 Answers

up vote 2 down vote accepted 
$arr = array("November, 2011", "May, 2011", "July, 2010");

// An array to hold the output
$outarr = array();

foreach ($arr as $pair) {
  // Split the month/year from each pair
  list($mon, $year) = explode(",", $pair);
  // Trim whitespace on the $year
  $year = trim($year);  

  // If the year key isn't set, create it now
  if (!isset($outarr[$year])) $outarr[$year] = array();

  // And append the month. Don't forget to trim whitespace!
  $outarr[$year][] = trim($mon);
}

The output:

print_r($outarr);
Array
(
    [ 2011] => Array
        (
            [0] => November
            [1] => May
        )

    [ 2010] => Array
        (
            [0] => July
        )  
)
share|improve this answer
Whitespace should be trimmed at least around year (not month) I think. – Frosty Z Nov 18 '11 at 21:49
1  
@FrostyZ oh yes, you're correct. added above. – Michael Berkowski Nov 18 '11 at 21:49
up vote 2 down vote 
<?php

$initialArray = array("November, 2011", "May, 2011", "July, 2010");

$finalArray = array();

foreach($initialArray as $value)
{
  // Note: I suppose here that each initialArray element is "<Month>, <Year>",
  // otherwise the following line may trigger errors.
  list($month, $year) = array_map('trim', explode(",", $value));

  if (!isset($finalArray[$year]))
    $finalArray[$year] = array();

  $finalArray[$year][] = $month;
}

// orders years, however months arrays below years won't be ordered.
ksort($finalArray);
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up vote 1 down vote

Try this (Edit 2nd pass, forgot keyword array, added trim):

$array = array("November, 2011", "May, 2011", "July, 2010");

foreach ($array as $element) {

    list($month, $year) = explode(',', $element);

    $years[trim($year)][] = trim($month);
}
share|improve this answer
Syntax error on your first line + a trim() should be applied to year keys – Frosty Z Nov 18 '11 at 21:52
1  
@FrostyZ: haha thanks. Forgot keyword array, it's what I get for doing it without testing. – Mike Purcell Nov 18 '11 at 21:57
up vote 1 down vote

Alright, let's try this:

<?php

$my_array = array('November, 2011', 'May, 2011', 'July, 2010');
$final = array();

foreach($my_array as $item) {

    // Let's split the Month and Year
    $item = explode(', ', $item);
    $final[$item[1]][] = $item[0];
}

print_r($final);

?>

The final output should be:

Array
(
    [2011] => Array
        (
            [0] => November
            [1] => May
        )

    [2010] => Array
        (
            [0] => July
        )

)
share|improve this answer

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