sort arrays c++

[MisterWhite]

So i'm curious is there a better way to sort many variables at the time when they are in a STRUCT.

If we have:

struct glove{    int sex;//  3 = male, 4 - female    int hand;// 1 - left , 2 - right    int size;};

and i'd like to sort by the sex, so that first would be all the males  ( 3 ), and then the females ( 4 ).

3 1 42 3 1 25 3 1 36 3 2 254 1 25 4 1 13 4 2 15 4 2 25 

so that i would not need to wrtite this:

for(int i=0; i<n-1; i++)    {        for(int j=1; j<n; j++)        {            if(p[i].sex>p[j].sex)            {                int num = p[i].sex;//THIS                p[i].sex=p[j].sex;//PART                p[j].sex=num;// HERE            }        }    }

for three times, is there a way to move all three elements at the same time?

[Sauron]

You're using what is known as bubble sort. There are way more efficient methods, but none is shorter to write.

 

For example you could use quick sort:

void quicksort(int *arr, int left, int right){    int min = (left+right)/2;    cout<<"QS:"<<left<<","<<right<<"\n";    int i = left;    int j = right;    int pivot = arr[min];    while(left<j || i<right)    {        while(arr[i]<pivot)        i++;        while(arr[j]>pivot)        j--;        if(i<=j){            swap(i,j,arr);            i++;            j--;        }        else{            if(left<j)                quicksort(arr, left, j);            if(i<right)                quicksort(arr,i,right);            return;        }    }}

[Nineshadow]

http://linustechtips.com/main/topic/422629-sorting-algorithms/

A thread of mine. The techniques can be easily implemented using templates.

Or use std::vector and its sorting algorithm which can be use a custom function.

 

STL ftw.

[MisterWhite]

 

You're using what is known as bubble sort. There are way more efficient methods, but none is shorter to write.

 

For example you could use quick sort:

void quicksort(int *arr, int left, int right){    int min = (left+right)/2;    cout<<"QS:"<<left<<","<<right<<"\n";    int i = left;    int j = right;    int pivot = arr[min];    while(left<j || i<right)    {        while(arr[i]<pivot)        i++;        while(arr[j]>pivot)        j--;        if(i<=j){            swap(i,j,arr);            i++;            j--;        }        else{            if(left<j)                quicksort(arr, left, j);            if(i<right)                quicksort(arr,i,right);            return;        }    }}

i dont really need other way to sort right now, just if i can sort 3 elements at the time

[Sauron]

i dont really need other way to sort right now, just if i can sort 3 elements at the time

 

no, because you can't know which elements are larger than the others before checking. @Nineshadow explains it pretty well, you'll see that there's no way you can make your code any shorter than that (why would you want to anyway?)

[MisterWhite]

no, because you can't know which elements are larger than the others before checking. @Nineshadow explains it pretty well, you'll see that there's no way you can make your code any shorter than that (why would you want to anyway?)

i hoped there was a way to to avoid writing this:

int num = p[i].sex;//THISp[i].sex=p[j].sex;//PARTp[j].sex=num;// HERE

for my three arrays in a struct, thought there might be a more logical way when they are in a struct.

 

EDIT:

now it looks like this:

    int sk = p[i].lytis;    p[i].lytis=p[j].lytis;     p[j].lytis=sk;    int sk1 = p[i].ranka;     p[i].ranka=p[j].ranka;     p[j].ranka=sk1;   int sk2 = p[i].dydis;   p[i].dydis=p[j].dydis;    p[j].dydis=sk2;

[Nineshadow]

Example using std::vector :

#include <iostream>#include <vector>#include <algorithm>using namespace std;struct glove{    int sex;//  3 = male, 4 - female    int hand;// 1 - left , 2 - right    int size;    glove(int s, int h , int sz)    {        sex = s;        hand = h;        size = sz;    }    void print()    {        cout << sex << ' ' << hand << ' ' << size << '\n';    }};struct comp_sex{    inline bool operator() (const glove& glove1, const glove& glove2)    {        return (glove1.sex < glove2.sex);    }};int main(){    vector<glove> v;    v.push_back(glove(3,1 , 42));    v.push_back(glove(4, 2 , 43));    v.push_back(glove(3, 1 , 27));    sort(v.begin(),v.end() , comp_sex() );    for(int i = 0; i < v.size() ; i++)    v[i].print();    return 0;}

[MisterWhite]

 

Example using vector :

#include <iostream>#include <vector>#include <algorithm>struct glove{    int sex;//  3 = male, 4 - female    int hand;// 1 - left , 2 - right    int size;    glove(int s, int h , int sz){ sex = s; hand = h; size = sz;}};struct comp_sex(){    inline bool operator() (const glove& glove1, const glove& glove2)    {        return (glove1.sex < glove2.sex);    }};int main(){    vector<glove> v;    v.push_back(glove(3,1 , 42));    v.push_back(glove(4, 2 , 43));    v.push_back(glove(3, 1 , 27));    sort(v.begin(),v.end() , comp_sex() );    return 0;}

i'm doing the exam exercises and i must use arrays. They dont teach us vectors.

[fizzlesticks]

i'm doing the exam exercises and i must use arrays. They dont teach us vectors.

As long as they're real arrays and not pointers, and you're using c++14, std::sort works on arrays too.

int arr[100] = blah blah blah;std::sort(std::begin(arr), std::end(arr), some_compare_function/struct/lambda);

Also std has a swap function that takes 2 of anything and swaps all their values. http://en.cppreference.com/w/cpp/algorithm/swap

 

Edit: unrelated but your glove constructor should really use an initializer list

struct glove{    int sex;//  3 = male, 4 - female    int hand;// 1 - left , 2 - right    int size;    glove(int s, int h , int sz)     : sex(s), hand(h), size(sz)     {}};

[MisterWhite]

 

As long as they're real arrays and not pointers, and you're using c++14, std::sort works on arrays too.

int arr[100] = blah blah blah;std::sort(std::begin(arr), std::end(arr), some_compare_function/struct/lambda);

Also std has a swap function that takes 2 of anything and swaps all their values. http://en.cppreference.com/w/cpp/algorithm/swap

 

Edit: unrelated but your glove constructor should really use an initializer list

struct glove{    int sex;//  3 = male, 4 - female    int hand;// 1 - left , 2 - right    int size;    glove(int s, int h , int sz)     : sex(s), hand(h), size(sz)     {}};

So sort(begin(arr), end(arr), arr>arr[j]) like this?

[fizzlesticks]

So sort(begin(arr), end(arr), arr>arr[j]) like this?

arr>arr[j] is just a bool. You need a function that can be called over and over that compares the sex of each glove. 

There are several ways to do it. You could create a callable struct like in Nineshadows example, overload operator< inside glove in which case you wont need the third parameter in the sort function or use a lambda. 

 

My preferred way is a lambda but if you haven't even learned vectors yet you probably shouldn't use something that advanced. But anyway it would look like this

std::sort(std::begin(gs), std::end(gs), [](const auto& g1, const auto& g2) noexcept { return g1.sex < g2.sex; });