CODEWITHSUNDEEP
c++
Justin D.
Justin D.

Reputation: 4976

C++ - Sorting with an extra parameter

I am working with an adjacency list and a map defined using the following type definitions :

typedef vector<list<Edge> > adjacencyList;
typedef map<int,WikiPage> idToWikiMap;

I would like to sort an adjacency list (adjacencyList) by name. The index of the adjacencyList is mapped to a pair in my map. For example,

adjacencyList lst;

lst[0] = NULL
lst[1] = list of edges related to City1
lst[2] = list of edges related to City2

idToWikiMap mymap;

mymap[1] -> Name of City1
mymap[2] -> Name of City2

So I want to sort the adjacency list using the name in the map related to the index of the adjacency list. I have come up with the following code. Since my compare function needs the map, I can't just create a normal function. So I used a struct and Local.

The compare works. I can cout the name of the lists currently being compared and the return value. For example, I get

Comparing Chicago and  New York
Smaller: 0
Comparing Montreal and  Chicago
Smaller: 1
Comparing Montreal and  New York
Smaller: 0
Comparing Toronto and  Chicago
Smaller: 1
Comparing Toronto and  Montreal
Smaller: 1
Comparing Toronto and  New York
Smaller: 1
Comparing Miami and  Chicago
Smaller: 1
Comparing Miami and  Montreal
Smaller: 0

However, the original does not get modified... Did I do something wrong?

  void printOrganized(adjacencyList& lst, idToWikiMap page_ofID) {
  // Define compare functions that accepts idToWikiMap parameter
  struct Local {
    Local(idToWikiMap mymap) { this->mymap = mymap; }

    bool operator() (const list<Edge>& l1, list<Edge>&l2)
    { return mymap.at(l1.front().origin).title < mymap.at(l2.front().origin).title; }

    idToWikiMap mymap;
  };

  /* Sort adjacenyList lst */
  sort (lst.begin()+1, lst.end(), Local(page_ofID));

  ...
  }

Upvotes: 0

Views: 141

Answers (1)

PaF
PaF

Reputation: 3477

Your code worked well for me, after I fixed a compilation error. Maybe your compiler isn't reporting this error, but it's causing your code not to work?

Anyway, the error is in the comparison function - you should get both parameters as const references, i.e.

bool operator() (const list<Edge>& l1, const list<Edge>& l2)

Also, I had to move Local to the global scope, because it wasn't working for me as long as it was defined inside the function. You can see the working result here: http://ideone.com/e.js/UPMeFm

Upvotes: 1

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