How to implement indexOf in solidity?

Question

In javascript, can use indexOf to get the index of the value.

const array = [2, 5, 9];
const index = array.indexOf(5); 

How to implement it in solidity? I'll get the value from another function, and I want to use that value to find the index in an array(_R2), then delete that value.

uint256[] internal _R2;

Answer 1

You simply have to loop over the values to find the one you are searching for.

Something like this:

function indexOf(uint256[] memory arr, uint256 searchFor) private returns (uint256) {
  for (uint256 i = 0; i < arr.length; i++) {
    if (arr[i] == searchFor) {
      return i;
    }
  }
  return -1; // not found
}

Answer 2

So, Lauri's answer was kind of correct, but array should be arr on line 3 and an unsigned int can never be -1 so I would rather revert on that line. Code should look like:

function indexOf(uint256[] memory arr, uint256 searchFor) private pure returns (uint256) {
    for (uint256 i = 0; i < arr.length; i++) {
      if (arr[i] == searchFor) {
        return i;
      }
    }
    revert("Not Found");
  }