[TOC] # 問題描述 我們想把數組 ~~~ $employees=[ [ 'name'=>'JellyBool', 'email'=>'jellybool@outlook.com', 'company'=>'Laravist Inc' ], [ 'name'=>'Taylor', 'email'=>'Taylor@laravel.com', 'company'=>'Laravel Inc' ] ]; ~~~ 變成下面這個樣子,name的值作為key,email的值為value ~~~ $lookup=[ 'JellyBool'=>'jellybool@outlook.com', 'Taylor'=>'Taylor@laravel.com', ]; ~~~ # 解決 ~~~ $emails=collect($employees)->map(function($employee){ $emailLookup=[]; $emailLookup[$employee['name']]=$employee['email']; return $emailLookup; }); dd($emails); ~~~ 這種是形成結構了,但是多了層數組 ~~~ Collection {#166 #items: array:2 [ 0 => array:1 [ "JellyBool" => "jellybool@outlook.com" ] 1 => array:1 [ "Taylor" => "Taylor@laravel.com" ] ] } ~~~ 如果我們使用flatten ~~~ $emails=collect($employees)->map(function($employee){ $emailLookup=[]; $emailLookup[$employee['name']]=$employee['email']; return $emailLookup; })->flatten(1); ~~~ key值就變了,是0,1不是我們的name ~~~ Collection {#159 #items: array:2 [ 0 => "jellybool@outlook.com" 1 => "Taylor@laravel.com" ] } ~~~ ## reduce 將集合縮減到單個數值，該方法會將每次迭代的結果傳入到下一次迭代 第一次迭代時 $carry 的數值為 null；然而你也可以傳入第二個參數進 reduce 以指定它的初始值： ~~~ $emails=collect($employees)->reduce(function($emailLookup,$employee){ $emailLookup[$employee['name']]=$employee['email']; return $emailLookup; },[]); dd($emails); ~~~