counting how many times an item appears in a multidimensional array in javascript

Question

Given a multidimensional array like this:

 var arr = [
\"apple\",
[\"banana\", \"strawberry\",\"dsffsd\", \"apple\"],
\"banana\",
[\"sdfdsf\",\"apple\",[\"apple\         


        

Answer 1

I think this is a simple approach but you can get tangled with it:

 function countItems(arr, item, count = 0){
     if(!arr.length) return count; //if the array is empty then there's nothing else to count
     let cTemp;
     if(Array.isArray(arr[0])){ //if the next item is an array
         cTemp = countItems(arr[0], item); //count the items in that array
     } else {
         cTemp = arr[0] === item ? 1 : 0; //if it's a string the compare it with item
         //1 if we found it
         //0 if we didn't
     }
     return countItems(arr.slice(1), item, count+cTemp);
     //count the items of the rest of the array and add what we found
     //arr.slice(1) is the rest of the array
     //cTemp is the count for the first item in the array
 }

Which of course can be rewritten into a single line:

 let countItems = ([first, ...rest], item, count = 0) => !first ? count : countItems(rest, item, count + (Array.isArray(first) ? countItems(first, item) : +(first === item)))