## James @ Minsoft

Member since: Tuesday, 29 January 2019
Profile viewed: 603 views Points: 2

James @ Minsoft replied to the topic 'set_difference' in the forum. 5 years ago

Here is an updated version with bugs removed;

I wish to find the set_difference between two vector containers with non-unique values.
The program below illustrates the problem. The answer I get is

data3.element1 = 1
data3.element1 = 2
data3.element1 = 2
data3.element1 = 4
data3.element1 = 4
data3.element1 = 5
data3.element1 = 5
data3.element1 = 0

whereas, the answer I want is;

data3.element1 = 1
data3.element1 = 5
data3.element1 = 5

i.e. all 2's and 4's removed. Any ideas how my code could be modified to do this?

Here is the current program example:

#include <vector>
#include <algorithm>
#include <iterator>
#include <iostream>

struct data {
int element1;
int element2;
};

int i, records;

std::vector<data> data1(10), data2(10), data3(10);

std::vector<data>::iterator it_difference;

struct difference {
bool operator()(const data& d1, const data& d2) const {
return (d1.element1 < d2.element1);
}
};

int main()
{

data1.element1 = 1;
data1.element1 = 2;
data1.element1 = 2;
data1.element1 = 2;
data1.element1 = 4;
data1.element1 = 4;
data1.element1 = 4;
data1.element1 = 5;
data1.element1 = 5;

data2.element1 = 2;
data2.element1 = 4;

it_difference = std::set_difference(data1.begin(), data1.end(),
data2.begin(), data2.end(),
data3.begin(), difference());

data3.resize(it_difference-data3.begin());

records = std::distance(data3.begin(), it_difference);

for(i = 0; i < records; i++)

std::cout << "data3[" <<i<<"].element1 = "<< data3.element1 << "\n";

}

James @ Minsoft created a new topic ' set_difference' in the forum. 5 years ago

Hello,

I have following code;

struct data {
int element1;
int element2;
};

vector<data> data1(5), data2(5), data3(5)

data1.element1 = 1;
data1.element1 = 2;
data1.element1 = 2;
data1.element1 = 3;
data1.element1 = 3;
data1.element1 = 4;

data2.element1 = 2;
data2.element1 = 3;

struct comp {

bool operator()(const data& data1, const data& data2) const
{
return (data1.element1 != data2.element1);
};

std::set_difference(data1.begin(), data1.end(), data2.begin(),
data2.end(), data3.begin(), comp());

The result I get is data3.element1 = {1,2,3,4}

The result I want is data3.element1 = {1,4}

i.e. I want all occurrences of 2 and 3 removed, not just the first ones.

I was wondering what modifications I could make to do this?

I prefer to do it in one pass of the set_difference command, as I need for it
to run as fast as possible.

Thankyou,

James

James @ Minsoft created a new topic ' STL set_intersection with classes' in the forum. 5 years ago

Hello,

I was wondering if set_intersection can be used with classes or does it only work with C++ types

e.g. I have following code with C++ classes;

struct data {
int field1
int commonfield
};

vector<data> data1(5), data2(5), data3(5)

struct comp { // -Checked 12-2-02

bool operator()(const data& lhs, const data& rhs) const

{

return (lhs.commonfield < rhs.commonfield);

}

};
std::set_intersection(data1.begin(), data1.end(), data2.begin(),
data2.end(), data3.begin(), comp());

Does this code then find the intersection based on commonfield, or can I only use C++ types e.g. vector<int> ?

James @ Minsoft created a new topic ' STL to speed up record removal' in the forum. 8 years ago

Hello,

I have some computer code which I want to speed up with STL. I was wondering if there is a faster implementation of the code presented.

I wish to delete all the elements in array1 which have matching elements in array2. array1 and array2 are not sorted, and I need
to preserve their orders after deletion.

vector<int> array1(1000), array2(20);

int array1_elements, array2_elements;

struct array_remove {

bool operator()(const int& rhs) const

{

return (rhs == -1);

}

k = array1_elements;

for(i = 1; i <= array1_elements; i++) {

for(j = 1; j <= array2_elements; j++) {

if(array1 == array2[j]) {

array1 = -1;

k--;

}

}

}

std::remove_if(array1.begin(), array1.begin() + array1_elements, array_remove());

array1_elements = k;

I was thinking of using 2 sorts and a while statement, but

I was wondering if STL could be used for a faster implementation.