Is there a faster way to search something in an array than in_array in PHP?

Question

I need to check some input string against a huge (and growing) list of strings coming from a CSV file (1000000+). I currently load every string in an array and check against it via in_array(). Code looks like this:

$filter = array();
$filter = ReadFromCSV();

$input = array("foo","bar" /* more elements... */);
foreach($input as $i){
  if(in_array($i,$filter)){
    // do stuff
  }
}

It already takes some time and I was wondering is there is a faster way to do this?

Maybe you should think about using a DB instead of reading the values from CSV into memory each time. — Hirnhamster
– Hirnhamster, Commented Aug 31, 2014 at 11:57

frankster · Accepted Answer · 2014-08-31 11:54:50Z

3

in_array() checks every element in the array until it finds a match. The average complexity is O(n).

Since you are comparing strings, you might store your input as array keys instead of values and look them up via array_key_exists(); which requires a constant time O(1).

Some code:

$filter = array();
$filter = ReadFromCSV();
$filter = array_flip($filter); // switch key <=> value

$input = array("foo","bar" /* more elements... */);
foreach($input as $i){
  if(array_key_exists($i,$filter)){ // array_key_exists();
    // do stuff
  }
}

answered Aug 31, 2014 at 11:54

frankster

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2 Comments

Shoruna Over a year ago

Wow.. that really makes a difference. Why can't in_array be that fast?

frankster Over a year ago

It only works that easy because you are comparing strings. Array key types are restricted to integer and string whereas array values can be anything.

giusc · Accepted Answer · 2014-08-31 12:03:47Z

0

That's what indexes were invented for.

It's not a matter of in_array() speed, as the data grows, you should probably consider using indexes by loading data into a real DBMS.

answered Aug 31, 2014 at 12:03

giusc

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