Sorting Lines - C++

[sadsdw]

Hi,

I would like to ask about sorting lines in C++, (4 columns = 3 columns of integers and the last one a string):

3 56 3 NA
7 50 5 NA
2 100 1 OK

I tried the function sort() using a vector of strings, but failed in cases like 120 10023, where 10023 was sorted first than 120.

Does anyone have some idea?

Cheers,

SADS

string sortPed(ofstream &myfileLog, vector<string> &vetorPed, ofstream &myfileOut)
{

	myfileLog << "\nSorting ..." << endl;
	sort(vetorPed.begin(), vetorPed.end());
	myfileLog << "SORTED! Printing ped file!" << endl;
	printV(myfileLog, vetorPed);
	printV(myfileOut, vetorPed);

}

[Narue]

It looks to me like you should be tokenizing the string into fields first, then using a specific field as the comparison data. std::sort() takes a third argument as a predicate, if you want to customize the comparison method:

#include <algorithm>
#include <fstream>
#include <iostream>
#include <string>
#include <vector>

using namespace std;

int main()
{
    ifstream in("test.txt");

    if (in) {
        vector<string> lines;
        string line;

        while (getline(in, line))
            lines.push_back(line);

        sort(lines.begin(), lines.end(), [](const string& a, const string& b) {
            // Use the first word for comparison
            return a.substr(0, a.find_first_of(' ')) <
                b.substr(0, b.find_first_of(' '));
        });

        for_each(lines.begin(), lines.end(), [](const string& s) { 
            cout << s << '\n'; 
        });
    }
}

[sadsdw]

Thanks for your help!

Basically, I'm not concern with the second, third and last column. The problem is just sort the first column correctly.

I will try use your code.

Cheers

[Narue]

The problem is just sort the first column correctly.

Convenient. That's precisely what my example does, but you need to have a C++0x friendly compiler. ;)

[sadsdw]

Hi Narue,

Thanks for your help ... You're correctly! I had problems of compilation ... :(

Do you have suggestions?

Cheers,

[Narue]

Do you have suggestions?

Don't use C++0x features?

#include <algorithm>
#include <fstream>
#include <iostream>
#include <string>
#include <vector>

using namespace std;

namespace {
    struct first_word {
        bool operator()(const string& a, const string& b)
        {
            return a.substr(0, a.find_first_of(' ')) <
                b.substr(0, b.find_first_of(' '));
        }
    };
}

int main()
{
    ifstream in("test.txt");
    vector<string> lines;
    string line;

    if (in) {
        while (getline(in, line))
            lines.push_back(line);

        sort(lines.begin(), lines.end(), first_word());

        for (vector<string>::const_iterator it = lines.begin(); it != lines.end(); ++it)
            cout << *it << '\n';
    }
}

[sadsdw]

Hi Narue,

I found the same problem:

Original file:

1005 2 3 NA
100004 1 4 NA
99 1 3 NA
909 3 5 NA
1 4 5 NA

Correct output:

1 4 5 NA
99 1 3 NA
909 3 5 NA
1005 2 3 NA
100004 1 4 NA

Output LAST CODE:
1 4 5 NA
100004 1 4 NA
1005 2 3 NA
909 3 5 NA
99 1 3 NA

This is the problem. Due the "0" in 100004, it's placed before than 1005 with lower number of "0"

[Narue]

That's the difference between a numeric comparison and a lexicographical comparison. Let's take 100004 and 1005 as an example. The fourth character of the former is 0 and the fourth character of the latter is 5, thus the first string is smaller because 0 is less than 5.

If you want those strings compared as numbers, then convert them to numbers.

[sadsdw]

Thanks Narue!

I'm trying to do this.

Cheers

[sadsdw]

Narue,

The problem is convert just the first column of my file. I could be created the vector of integer instead of string. Due this problem (Last column is string) I'm trying other solution.

Cheers,