function getIndex(arr, key) {
            var result = -1;
            arr.some(function (entry, index) {
                if (entry[0] === key) {
                    result = index;
                    return true;
                }
                return false;
            });
            return result;
        }
Returns index in provided array that matches the specified key.

@param {Array<Array>} arr
@param {*} key
@returns {number}