human
Solve the following python programming problem given the following code:
def indexBy(self, val = None) : 
    "
        Indexes the object's values by a criterion, similar to
        `groupBy`, but for when you know that your index values will be unique.
        " 
    if (val is None) : 
        val = (lambda * args : args [0]) 
def by(result, key, value) : 
        result [key] = value 
res = self._group (self.obj, val, val) 
    return self._wrap (res) 

    
    

    Fix the buggy line: res = self._group (self.obj, val, val)
assistant
#Here is Python program to fix the buggy line: res = self.

res = self._group (self.obj, val, def by()