A function is a relation from a set of inputs to a set of possible outputs where each input is related to exactly one output.
In the given relation {(-2,4), (0,2), (-1,3), (4,-2)}, each input is mapped to exactly only one output.
So, the set of ordered pairs above is a function.
In the mapping diagram, each element in the domain is mapped exactly only to one element in the range. So, the mapping diagram is a function.
Consider the function
For each value of x, it gives exactly one value for y. Hence the given relation is a function.
From the table, -1 maps to both 2 and 4. Hence it is not a function.