How to Sort a Vector of User-Defined Types by Specific Variables?

Sort User-Defined Types in a Vector by Specific Variables

In order to sort a vector of user-defined types by a specific variable, you have two options: using the standard library sort or implementing your own sort function.

Using the Standard Library Sort

The standard library sort can be used if your user-defined type implements the "bool operator < (const Type& other) const" and a copy constructor. The comparison operator should define a meaningful way to compare the types. Here's an example:

struct MyType {
    int a;
    int b;
    bool operator<(const MyType& other) const {
        // Compare types based on a specific variable (e.g., a)
        return a < other.a;
    }
};

Using a Custom Sort Function

Alternatively, you can provide a custom ordering function or functor as the third argument to sort() instead of implementing the comparison operator. This function should compare the types based on the desired variable. For instance:

bool type_is_less(const MyType& t1, const MyType& t2) {
    return t1.a < t2.a;
}

std::sort(moo.begin(), moo.end(), type_is_less);

This approach is useful when:

• You cannot or do not want to implement the comparison operator.
• You need to sort built-in or pointer types that cannot be overloaded.
• You want to sort the sequence using different criteria at different times.

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