How to sort multiple arrays that contain data associated to each other via index

Question

I have a set of arrays with cities, countries, latitudes, and latitudes. c++ language.

ifstream file("worldcities.csv");
getline(file, temporay);
//inputs the file into 4 arrays for each catergories
for (i=0;getline(file,(cities[i]),',');i++)
{
getline(file, countries[i], ',');
getline(file, latitude[i], ',') ;
getline(file, longitude[i]);
}

How do i sort the array of latitudes and longitudes at the same time to find top five lowest or highest to all the others on the list but at the same time do no lose the elements of cities and countries those lats n longs are associated with?

It would be much easier if you combined city, country, lat, long into a structure or class, and then used a single array (or better, vector). — Paul R, Oct 09 '13 at 19:12
how would i do that? haven't really worked with vector or structures yet. — VKid, Oct 09 '13 at 19:13
The best solution is "don't use parallel arrays": aggregrate all the information into a list (or vector) of records instead. — paulsm4, Oct 09 '13 at 19:13
@user2770315 You google "c(++) struct tutorial" (or read a beginners' book), then you google "`std::vector` documentation", and you'll be good to do. — , Oct 09 '13 at 19:14

score 5 · Answer 1 · edited May 23 '17 at 11:57

5

"at the same time do not lose the elements of cities and countries those lats n longs are associated with"

When these are the values that belong together, why haven't you bundled them within a single object? i.e.:

struct Location {
    std::string city, country;
    double lng, lat;
};

and once you load all locations into the std::vector<Location> then you could just define own comparator and use std::sort.

This question might help you: How to use std::sort with a vector of structures and compare function?

edited May 23 '17 at 11:57

Community

1
1

answered Oct 09 '13 at 19:14

LihO

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confused on how to load it into struct from cvs file and then intilizing the variables. – VKid Oct 09 '13 at 19:17
1

@user2770315: [This question](http://stackoverflow.com/q/16446665/1168156) was first hit when I was looking for "reading values from CSV file in C++". – LihO Oct 09 '13 at 19:20

Zac Howland · Answer 2 · 2013-10-09T19:47:38.277

0

If you create a class or a struct that holds your data together (instead of associating them via array indexes), you will find it much easier to manage:

struct Details
{
    std::string city;
    std::string country;
    double latitude;
    double longitude;
};

struct csv_reader : std::ctype<char>
{
    csv_reader() : std::ctype<char>(get_table()) {}

    static std::ctype_base::mask const* get_table()
    {
        static std::vector<std::ctype_base::mask> rc(table_size, std::ctype_base::mask());
        rc[','] = std::ctype_base::space;
        rc['\n'] = std::ctype_base::space;
        return &rc[0];
    }
};

// in your program logic
std::ifstream fin("worldcities.csv");
std::vector<Details> vecDetails;
std::string line;
csv_reader reader;
while (std::getline(fin, line))
{
    std::istringstream iss(line);
    iss.imbue(std::locale(std::locale(), &csv_reader));
    Details d;
    iss >> d.city >> d.country >> d.latitude >> d.longitude;
    vecDetails.push_back(d);
}

// to sort by latitude
std::sort(vecDetails.begin(), vecDetails.end(), [](const Details& l, const Details& r)
{
    return l.latitude < r.latitude;
});

edited Oct 09 '13 at 19:47

answered Oct 09 '13 at 19:27

Zac Howland

15,777
1
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what is the library for locale and cvs reader? it is giving me a error. – VKid Oct 09 '13 at 19:33
error C2275: 'main::csv_reader' : illegal use of this type as an expression – VKid Oct 09 '13 at 19:37
You have to include `` ... and I missed a typo. Fixed. – Zac Howland Oct 09 '13 at 19:45
iss.imbue(std::locale(std::locale(), csv_reader)); <<---giving me sytax error on locale and cvs_reader – VKid Oct 09 '13 at 19:46
main::csv_reader' : illegal use of this type as an expression – VKid Oct 09 '13 at 19:47
It should not be inside main. I did miss the typo (missing `&`) in the original post. – Zac Howland Oct 09 '13 at 19:48
while (std::getline(fin, line)) << Error: expected a declaration – VKid Oct 09 '13 at 19:50
look 4 lines above for the declaration of `fin` ... `std::getline` is defined in ``, which you should have already included. – Zac Howland Oct 09 '13 at 19:59
yeah, i have #include , but still have sytax error for the while – VKid Oct 09 '13 at 20:03
Do you have `using namespace std;` somewhere in your code? What is the full error message? – Zac Howland Oct 09 '13 at 20:05
Either remove the `using namespace std;` or remove `std::` from the front of the standard functions. – Zac Howland Oct 09 '13 at 20:18

How to sort multiple arrays that contain data associated to each other via index

2 Answers2