Changing elements of lists
 

I am reading lines from a CSV and don't know what size it'll be, so I place read lines into a list of a structure "obs". Then I want to iterate through this list, put it into another list and then modify contents of the original list so that I can print that later. I am, however, not sure if I'm actually modifying the original.

using namespace std;

struct obs{

        int date;

        int p;

        int attr_price;

        int q;

        double bcode;

        double uniq_store_id;

};



int main(){

        string line;

        ifstream fdata("jumboa_corrected.csv");

        obs last_obs;

        getline(fdata,line);

        int scanned = sscanf(line.c_str(),"%i,%i,%i, %lf, %lf",&last_obs.q,&last_obs.date,&last_obs.p,

                &last_obs.bcode,&last_obs.uniq_store_id);

        list<obs> this_series(1,last_obs);

        obs this_obs;

        while(getline(fdata,line)){

                ++gi;

                sscanf(line.c_str(),"%i, %i,%i, %lf, %lf",&this_obs.q,&this_obs.date,&this_obs.p,&this_obs.bcode,&this_obs.uniq_store_id);

                this_series.push_front(this_obs);



... stuff that fills in a bunch of this_obs into the list

        if(condition to start unloading){

                list<obs*> qtr_ser_obs;

                for (list<obs>::reverse_iterator it=this_series.rbegin() ; it != this_series.rend(); ++it )

                {

                        qtr_ser_obs.push_front(&*it);

                         for (list<obs*>::reverse_iterator qtr_obs_it =qtr_ser_obs.rbegin(); qtr_obs_it !=qtr_ser_obs.rend();qtr_obs_it++){

                                (*qtr_obs_it)->attr_price= computed_attr_price;

                        }

                  }

}

In this last line, what am I modifying?
Any help would be greatly appreciated. I guess I'm really not sure what is being placed with the line "

qtr_ser_obs.push_front(&*it);

"

Re: Changing elements of lists
 

Welcome wiczerd,

wiczerd said,
Print the list after modification. However, there is no reason to add list item into another list to modify and see; qtr_ser_obs list will add more and more list items and the inner loop is started from the very first element - qtr_ser_obs.rbegin().

list<obs*> qtr_ser_obs;

for (list<obs>::reverse_iterator it=this_series.rbegin() ; it != 

                              this_series.rend(); ++it )

 {

    qtr_ser_obs.push_front(&*it);

    for (list<obs*>::reverse_iterator qtr_obs_it =qtr_ser_obs.rbegin

                 (); qtr_obs_it !=qtr_ser_obs.rend();qtr_obs_it++)

          {

        (*qtr_obs_it)->attr_price= computed_attr_price;

                }

   }

I think it should be:

for (list<obs>::reverse_iterator it=this_series.rbegin() ; it != 

                              this_series.rend(); ++it )

 {

    list<obs*> qtr_ser_obs;

    qtr_ser_obs.push_front(&*it);

    for (list<obs*>::reverse_iterator qtr_obs_it =qtr_ser_obs.rbegin

                 (); qtr_obs_it !=qtr_ser_obs.rend();qtr_obs_it++)

          {

        (*qtr_obs_it)->attr_price= computed_attr_price;

                }

   }

Re: Changing elements of lists
 

Thanks very much. The suggestion to print my list was very helpful, and it seems that I am modifying the original objects.
My syntax got a bit screwed up because I tried cutting and pasting from a much larger program, but your catch was good.
The reason I am moving things from one list to the other is because I need to do calculations on a moving window of the data in the larger list. So I was reading everything into the larger list, and then putting snippets into the smaller one and hoping to modify the initial obs by referencing them through the subset list.