php undefined index..using isset（）with is_array（）

This is my code:

if(is_array($ItemAttr["Actor"])){
  $Actors = implode(", ", $ItemAttr["Actor"]);
} else {
  $Actors = $ItemAttr["Actor"];
}

I'm getting undefined index: Actor in **line 1** and **line 3**

I guess i should use isset() function. Can anyone tell me how to combine that function with is_array() function..?

Not sure if this is what you mean but:

if( isset($ItemAttr["Actor"]) && is_array($ItemAttr["Actor"])){
    ....
}

In this case you are checking if the index exist before accessing its value.