array_walk or array_map?

Question

I'm currently using array_map to apply callbacks to elements of an array. But I want to be able to pass an argument to the callback function like array_walk does. I suppose I could just use array_walk, but I need the return value to be an array like if you use array_map, not TRUE or FALSE.

So is it possible to use array_map and pass an argument to the callback function? Or perhaps make the array_walk return an array instead of boolean?

http://stackoverflow.com/questions/3432257/difference-between-array-map-array-walk-and-array-filter — Jürgen Paul, Apr 12 '12 at 20:38

score 7 · Accepted Answer · answered May 10 '11 at 16:18

7

You don't need it to return an array.

Instead of:

$newArray = array_function_you_are_looking_for($oldArray, $funcName);

It's:

$newArray = $oldArray;
array_walk($newArray, $funcName);

answered May 10 '11 at 16:18

Lightness Races in Orbit

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But if I use `array_walk` the return value will be TRUE of FALSE. I want the return value to be an array like how `array_map` does. So either find a way to pass an argument using `array_map` or find a way so that `array_walk` return array instead of boolean. – Kemal Fadillah May 10 '11 at 16:38
1

Does `array_walk` edit the original array on which it is called? Because if it does, this is pretty sweet. – sdleihssirhc May 10 '11 at 16:41
that's because array_walk SETS the array. Try print_r($newArray); afterwards. Notice that Tomalak is NOT doing `$arr = array_walk($newArray, $funcName);` TRUE simply means 'it worked' and you can use the array that you inserted. – Joshua - Pendo May 10 '11 at 16:42
@sdleihssirhc Yes, the array_walk modify the original array. That is why I need it to return an array instead of boolean. – Kemal Fadillah May 10 '11 at 16:47
@PENDO Doesn't that kind of depend on the function that's supplied? I messed around with `array_walk`, and it only modified the original array if the "walker" function that I defined used the `&` symbol: `function walker(&$val) { ... }` – sdleihssirhc May 10 '11 at 16:52
the example above does what you want.... (1) first copy your original `$newArray = $originalArray;` .. (2) Alter the copier one `array_walk($newArray, 'function');` .. (3) use the new array `print_r($newArray);` .. perhaps we're missing some info, but this is what you need? – Joshua - Pendo May 10 '11 at 16:56
@Kemal: I'm just repeating my answer here but... you _don't need it to return an array_. It doesn't return an array, so you need something equivalent. That's what my code does. Study it in detail and you'll see that it solves your problem. Do you think `array_walk` would even exist, if it only returned `TRUE` or `FALSE` and had no other effect? – Lightness Races in Orbit May 10 '11 at 17:39
@Kemal: `array_walk` modifies the array passed to it, but in my example that is _NOT_ your original array. It's a copy. It's just the same as if the function returned a new, modified array for you. – Lightness Races in Orbit May 10 '11 at 17:41

score 6 · Answer 2 · answered Oct 04 '13 at 06:19

6

If you want return value is an array, just use array_map. To add additional parameters to array_map use "use", ex:

array_map(function($v) use ($tmp) { return $v * $tmp; }, $array);

or

array_map(function($v) use ($a, $b) { return $a * $b; }, $array);

answered Oct 04 '13 at 06:19

Hieu Vo

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sdleihssirhc · Answer 3 · 2011-05-10T16:38:52.447

2

Depending on what kind of arguments you need to pass, you could create a wrapped function:

$arr = array(2, 4, 6, 8);
function mapper($val, $constant) {
    return $val * $constant;
}

$constant = 3;
function wrapper($val) {
    return mapper($val, $GLOBALS['constant']);
}

$arr = array_map('wrapper', $arr);

This actually seems too simple to be true. I suspect we'll need more context to really be able to help.

edited May 10 '11 at 16:38

answered May 10 '11 at 16:18

sdleihssirhc

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score 0 · Answer 4 · answered Mar 27 '17 at 19:14

To expand a bit on Hieu's great answer, you can also use the $key => $value pairs of the original array. Here's an example with some code borrowed from comment section http://php.net/manual/en/function.array-map.php

The following will use 'use' and include an additional parameter which is a new array.

Below code will grab "b_value" and "d_value" and put into a new array $new_arr (useless example to show a point)

// original array
$arr = ("a" => "b_value",
"c" => "d_value"); 

// new array
$new_arr = array();

array_map(function($k,$v) use (&$new_arr) { $new_arr[] = $v;}, array_keys($arr), $arr);

^ $k is key and $v is value

print_r of $new_arr is

Array
(
    [0] => b_value
    [1] => d_value
)

array_walk or array_map?

4 Answers4