C++ vector of class custom sort

Question

I have C++ code. There is a vector of class. I need to sort this vector in a bit custom way.

Here is my class:

class Sales
{
   public:
      string customer_name;
      string category;
      string aircraft;
      string day;
      string time;
      int week;
      int ticket_price;
      string payment;

   public:
      Sales () { 
         customer_name = "";
         category = "";
         aircraft = "";
         day = "";
         time = "";
         week = 0;
         ticket_price = 0;
         payment = "";
      }

      Sales (string f_cat, string airc, string xday, string xtime, int xweek) {
         customer_name = "";
         category = f_cat;
         aircraft = airc;
         day = xday;
         time = xtime;
         week = xweek;
         ticket_price = 0;
         payment = "";
      }  
};

Lets say we have:

vector <Sales> list;

Imagine that list has got populated record And I want to get this sorted like below logic:

sort_string = day + time + week + category + aircraft;

Example records:

Sunday, 12:00, 1, Comm, b777
Monday, 10:00, 1, Comm, b777
Monday, 10:00, 1, Comm, a321
Monday, 12:00, 1, Comm, a321
Friday, 09:00, 1, Comm, a321

Expected Sort:

Monday, 10:00, 1, Comm, a321
Monday, 10:00, 1, Comm, b777
Monday, 12:00, 1, Comm, a321
Friday, 09:00, 1, Comm, a321
Sunday, 12:00, 1, Comm, b777

Is this possible? if Yes, then how?

Thanks.

Kiril Kirov · Accepted Answer · 2013-11-21 12:54:31Z

7

Yes, it is.

Define

bool Sales::operator<( const Sales& other ) // member

or

bool operator<( const Sales& lhs, const Sales& rhs) // global

and use std::sort.

Example with only two int variables, as they are the easiest ones:

bool operator<( const Sales& lhs, const Sales& rhs)
{
    if( lhs.week < rhs.week ) 
         return true;
    else if( lhs.week > rhs.week )  
         return false;

    if( lhs.price < rhs.price ) 
         return true;
    else if( lhs.price > rhs.price )  
         return false;

    // ...

    return false;
}

Of course, your definition will be more complicated, because the other fields are more complicated for comparing (the weekday for example), but I hope you get the point.

Then:

#include <algorithm>
// ...
std::sort( list.begin(), list.end() );

By the way, list is bad name for variable, as it may conflict with std::list in some cases.

edited Nov 21, 2013 at 12:54

answered Nov 21, 2013 at 12:10

Kiril Kirov

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16 Comments

Oscar Over a year ago

how str::sort will know which variables to use in which order?

Chris L Over a year ago

You define it in the body of the functions listed by Kiril above.

Oscar Over a year ago

@ChrisL I am not familiar with this. Could you provide me an example?

Chris L Over a year ago

This isn't exactly what you need but an example. If you wanted to sort by week, then you'd define bool operator<( const Sales& lsh, const Sales& rhs) { return (lhs.week < rhs.week); } //ie if the week is less on the left than the right return true else false. This logic is used by std::sort to order your container

Chris L Over a year ago

@kiril looks good to me - saves me writing it in a comment, i've upvoted your answer now.

|

Boris Ivanov · Accepted Answer · 2013-11-21 14:13:12Z

0

if you will implement boolean function as member it must be const type

    bool operator<( const Sales& rhs) const{ 
        if (customer_name < rhs.customer_name ) return true; 
        if (category < rhs.category ) return true; 
        return false;
    }

See working example

answered Nov 21, 2013 at 14:13

Boris Ivanov

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4 Comments

Kiril Kirov Over a year ago

Why "must" ? Maybe "should"?

Boris Ivanov Over a year ago

It was not compiling for me until I put it.

Oscar Over a year ago

@BorisIvanov this is what I get when I compile test.cpp:73: error: a function-definition is not allowed here before ':' token because of for loops

Boris Ivanov Over a year ago

/usr/include/c++/4.8/bits/stl_algo.h:2269:19: error: passing ‘const Sales’ as ‘this’ argument of ‘bool Sales::operator<(const Sales&)’ discards qualifiers [-fpermissive] while (__pivot < *__last)

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