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firemonkeyc++builder

Pick columns from csv (FMX, C++)

I am reading one column of data out of a big CSV file (column 3). I want to know if there is a more efficient way of doing this. Right now i read each entire row, and then pick out my column. 

String S;
TStringList *List = new TStringList;
List->LoadFromFile(myCSV); // load the CSV file
std::auto_ptr<TStringList>pListA(new TStringList);
for (int i = 0; i < 400; i++) {   // for testing just getting first 400 rows.  
pListA->Text = StringReplace(List[0].Strings[i], ",", "\r\n", TReplaceFlags() << rfReplaceAll); 
S = pListA->Strings[3];  
// do something with this value from column 3
}

This code works fine, but it has to read the entire row of CSV data just to let me get that one column. Below is sample of the first 2 rows from the CSV data:

1,0,-6856,12830,8458,-16666,98717,-10718,-80874,49999,-99998,98569,99998,1,1,1,1,0,1,0,0,0,0,0,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,0,0,1,0,1,0,0,0,0,0,0,0,0,0,0,1,0,1,0,1,0,0,1,0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,0,0,0,0,1,0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0

2,8948,-6856,12830,8458,-16666,39641,63125,-99973,99998,-99998,39385,99998,1,1,1,1,0,1,0,0,0,0,0,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,0,0,1,0,1,0,0,0,0,0,0,0,0,0,0,1,0,1,0,1,0,0,1,0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,0,0,0,0,1,0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0

UPDATE: Based on Remy's code I ended up with this below. 

    TStreamReader* Reader;
    Reader = new TStreamReader(myCSV);
    while (!Reader->EndOfStream)
     {
     String S = Reader->ReadLine();
     int start = PosEx(_D(","), S, 1);
     start = PosEx(_D(","), S, start+1) + 1;
     int end = PosEx(_D(","), S, start);
     S = S.SubString1(start, end-start);
             // use S 
     }
    Reader->Close();
    delete Reader->BaseStream;
    delete Reader;
Solution

  • Instead of using TStringList at all, you could use TStreamReader to read each line, and simply parse each line using Strutils::PosEx() and String::SubString1() to extract just the 3rd column value.

    // NOTE: in C++11 and later, use std::unique_ptr instead!
std::auto_ptr<TStreamReader> Reader(new TStreamReader(myCSV)); // load the CSV file
while (!Reader->EndOfStream)
{
    String S = Reader->ReadLine();
    int start = PosEx(_D(","), S, 1);
    start = PosEx(_D(","), S, start+1) + 1;
    int end = PosEx(_D(","), S, start);
    S = S.SubString1(start, end-start);
    // do something with this value from column 3
}