variable of function within a function is not being recognized

Question

So i have this function that works great at adding up the sum of all values of a specific field in an array, in this case num_sold

So the array is something like this

array(4) {
  [0]=>
  array(2) {
    ["num_sold"]=>
    string(1) "6"
    ["id_product"]=>
    string(1) "2"
  }
  [1]=>
  array(2) {
    ["num_sold"]=>
    string(1) "6"
    ["id_product"]=>
    string(1) "3"
  }
  [2]=>
  array(2) {
    ["num_sold"]=>
    string(1) "4"
    ["id_product"]=>
    string(1) "4"
  }
  [3]=>
  array(2) {
    ["num_sold"]=>
    string(1) "5"
    ["id_product"]=>
    string(1) "7"
  }
}

// this correctly returns 21
$total = array_sum(array_map(
        function($element){
            return $element['num_sold'];
        },
        $array));

Now i want to be able to reuse this function on other field names so i wanted to create a function however the $field value isn't getting through. In php storm it says the $field value in sumFieldArray($field,$array) is not used anywhere but its clearly in the function.

I'm guessing it might be a scope issue so i tried doing global $field on the first line but that made no difference and instead it now says the global $field is not used anywhere. What am i doing wrong.

public static function sumFieldArray($field,$array)
    {
        $field_sum = array_sum(array_map(
            function($element, $field){
                return $element[$field];
            },
            $array));
        return $field_sum;
    }

php has exactly two scopes: global (top-level of your code), and local - within the current block. a variable defined at some intermediate level is essentially totally inaccessible, since global goes ONLY to the absolute top-level scope. there's no parent $var or grandparent $var scoping ability. — Marc B
– Marc B, Commented Dec 10, 2015 at 21:43
@MarcB You're forgetting the use() option in function expressions. — Barmar
– Barmar, Commented Dec 10, 2015 at 21:43
@barmar: ah yeah, true enough. but that's something that has to be done in the parent scope. a child can't reach back and fetch that stuff. — Marc B
– Marc B, Commented Dec 10, 2015 at 21:45

Ihor Burlachenko · Accepted Answer · 2015-12-10 21:46:32Z

2

You are right, this is a scope issue. You have to inherit parent scope with use.

public static function sumFieldArray($field, $array)
{
    $field_sum = array_sum(array_map(
        function($element, $field) use ($field) {
            return $element[$field];
        },
        $array));
    return $field_sum;
}

More information here: http://php.net/manual/en/functions.anonymous.php

answered Dec 10, 2015 at 21:46

Ihor Burlachenko

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Barmar · Accepted Answer · 2015-12-10 22:13:45Z

2

array_sum() calls the function with only one argument, the array element. It won't pass $field as the second argument. You can use the use() option to allow the inner function to access a variable in the outside scope.

public static function sumFieldArray($field,$array)
    {
        $field_sum = array_sum(array_map(
            function ($element) use($field) {
                return $element[$field];
            },
            $array));
        return $field_sum;
    }

If you're using PHP 5.5+, you can also use the array_column function to extract all the values of that field.

public static function sumFieldArray($field,$array)
    {
        return array_sum(array_column($array, $field));
    }

edited Dec 10, 2015 at 22:13

answered Dec 10, 2015 at 21:43

Barmar

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2 Comments

user1547410 Over a year ago

This would have been my preferred answer since it gives that useful array_column version even though that didn't work for me as i dont have php 5.5 others will find it useful however that code isnt valid. In php storm it says it expects ( after function so doing "function use($field) ($element){" will not work. I imagine it just needs a quick tweak and it will be a useful answer, appreciate the help.

Barmar Over a year ago

I had the use option in the wrong place, it goes after the argument list.

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