Make another array from one array

Question

I got this array in PHP:

$arr =('1-1.jpg','1-2.jpg','11-3.jpg', '1-4.jpg', '3-5.jpg', '41-5.jpg','1-3.jpg','4-5.jpg','14-5.jpg','54-5.jpg','64-5.jpg','14-5.jpg', '1-5.jpg');

I need this array, but I have PHP 5.27 version on the server :(

$newarray=('1-1.jpg','1-2.jpg','1-3.jpg', '1-4.jpg', '1-5.jpg');

Forget the server version, the criteria is "1-". How do I get all elements that is starting only with "1-"?

It's not obvious how to reduce the big array to the small one. What is the criteria? PS: "but i have php 5.27 version on server :(" --- anything particularly wrong with 5.2.7? — zerkms
– zerkms, Commented Aug 13, 2012 at 20:48
@zerkms It is obvious for me. (I think 5.2.7 doesn't have [...], you have to use array(...).) — uınbɐɥs
– uınbɐɥs, Commented Aug 13, 2012 at 20:49
Like zerkms, you need to give us substantially more information than you've given us. — David
– David, Commented Aug 13, 2012 at 20:49
Do a string comparison on each element. If it matches the pattern you're looking for, add it to the second array. It's really not that complicated. — Matt
– Matt, Commented Aug 13, 2012 at 20:53

uınbɐɥs · Accepted Answer · 2012-08-13 20:53:24Z

4

Use this code:

<?php
$arr = array('1-1.jpg','1-2.jpg','11-3.jpg', '1-4.jpg', '3-5.jpg', '41-5.jpg','1-3.jpg','4-5.jpg','14-5.jpg','54-5.jpg','64-5.jpg','14-5.jpg', '1-5.jpg');
$newarray = array();
foreach($arr as $item) {
    if(substr($item, 0, 2) == '1-') $newarray[] = $item;
}
sort($newarray); // Add this to sort the array
?>

You can use the sort function after the foreach to sort the array.

answered Aug 13, 2012 at 20:53

uınbɐɥs

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4 Comments

David Over a year ago

It's not every day the first two answers have exactly the same technique :)

zerkms Over a year ago

"exactly the same technique" -- what amazing is in using substr for getting substring? The same answers happen a lot every day (for such trivial questions)

David Over a year ago

Tough crowd today. I was observing that @ShaquinTrifonoff had basically the same code within a couple seconds of each other.

uınbɐɥs Over a year ago

@David - Normally with an easy question like this I will end up with the 1 New answer has been posted message when I am typing my answer.

goat · Accepted Answer · 2012-08-13 22:07:21Z

1

Use preg_grep

$arr = array('1-1.jpg','1-2.jpg','11-3.jpg', '1-4.jpg', '3-5.jpg', '41-5.jpg','1-3.jpg','4-5.jpg','14-5.jpg','54-5.jpg','64-5.jpg','14-5.jpg', '1-5.jpg');

print_r(preg_grep('#^1-#', $arr));

demo: http://codepad.org/ipDmYEBI

answered Aug 13, 2012 at 22:07

goat

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6 Comments

Alex Kalicki Over a year ago

I'm trying to learn regex but I can't figure out what the # symbols are for. Wouldn't preg_grep('/^1-/', $arr) work, without the hashtags? Thanks! This seems much nicer than doing it by substring.

goat Over a year ago

@AlexKalicki, in php(and maybe perl too) the way you specify the regex pattern, you use pattern delimiters to separate the pattern from pattern option flags. In general, resources that teach regex don't talk much about this because its not common to all regex implementations in various programming languages. But yes, it would work correctly using / instead of #, but I use # out of habit because / often occurs as a litterla character in the pattern, and then you need to escape it with a backslash....and then its ugly to read.

Alex Kalicki Over a year ago

Ah, got it. I knew about using pattern delimiters in PHP, but I didn't know there were more options for what you use than just forward slashes. :)

uınbɐɥs Over a year ago

Some info: On average, when measured with microtime(true);, this method takes 4.6968460083008E-5 amount of time, the substr(); method (like my answer) takes 4.1007995605469E-5.

goat Over a year ago

@ShaquinTrifonoff, interesting. I bet you though, that preg_grep pulls ahead on larger arrays. regex in php has a one-time overhead per pattern to compile the regex, but after that, everything executes in optimized c code, while your method is constantly switching between user interpreted php, and c code.

|

Alex Kalicki · Accepted Answer · 2012-08-13 22:21:49Z

1

Another way would be to use PHP's array_filter method:

$arr = array('1-1.jpg','1-2.jpg','11-3.jpg', '1-4.jpg', '3-5.jpg', '41-5.jpg','1-3.jpg','4-5.jpg','14-5.jpg','54-5.jpg','64-5.jpg','14-5.jpg', '1-5.jpg');
$newArr = array_filter($arr, "filterArray"); // stores the filtered array

function filterArray($value){
    return (substr($value, 0, 2) == "1-");
}

answered Aug 13, 2012 at 22:21

Alex Kalicki

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1 Comment

uınbɐɥs Over a year ago

I was just about to post another answer with this :-)

David · Accepted Answer · 2012-08-13 21:02:10Z

0

<?php
$new_array = array();
foreach ($old_array as $line) {
   if (substr($line, 0, 2) == "1-") {
      $new_array[] = $line;
   }
}
?>

This checks to see if the first two characters of each element is 1-, and if it is, adds it to the new array.

edited Aug 13, 2012 at 21:02

answered Aug 13, 2012 at 20:54

David

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3 Comments

Miomir Dancevic Over a year ago

After this i got this Array ( [0] => 2-1.jpg [1] => 3-1.jpg [2] => 4-1.jpg [3] => 5-1.jpg [4] => 6-1.jpg )

uınbɐɥs Over a year ago

@MiomirDancevic That's because this method adds every value that does not start with 1-. See my answer.

uınbɐɥs Over a year ago

@David - The end result should be Array('1-1.jpg','1-2.jpg','1-3.jpg', '1-4.jpg', '1-5.jpg').

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