How to create a flat JSON Object instead of array of objects in PHP -

i trying create flat json object 3 arrays in php. output of following code object containing array of objects:

{  "amphibian":[      {"frogs":"green"}   ],  "mammal":[     {"bats":"black"},     {"elephants":"grey"},     {"rats":"black"},     {"turtles":"green"}   ] } 

however, not want. possible turn output object containing flat objects during loop? desired output :

{   "amphibian":     {"frogs":"green"},   "mammal":       {"bats":"black","elephants":"grey","rats":"black","turtles":"green"} } 

here's code:

$colors = array("frogs"=>"green","bats"=>"black","elephants"=>"grey","rats"=>"black","turtles"=>"green");  $allanimals = array("frogs","bats","elephants","rats","turtles");  $group = array("frogs"=>"amphibian","bats"=>"mammal");  $output = array();  foreach($allanimals $key=>$animal){      if(isset($group[$animal])){          $grouptitle = $group[$animal];     }      $output[$grouptitle][] = array($animal=>$colors[$animal]);  }  print json_encode($output); 

modify $output[$grouptitle][$animal] = $colors[$animal];

$colors = array("frogs"=>"green","bats"=>"black","elephants"=>"grey","rats"=>"black","turtles"=>"green");      $allanimals = array("frogs","bats","elephants","rats","turtles");      $group = array("frogs"=>"amphibian","bats"=>"mammal");  $output = array();      foreach($allanimals $key=>$animal){   if(isset($group[$animal])){     $grouptitle = $group[$animal];   }   $output[$grouptitle][$animal] = $colors[$animal]; //here }  print json_encode($output); 

output:

{ "amphibian":{"frogs":"green"}, "mammal":{"bats":"black","elephants":"grey","rats":"black","turtles":"green"} }