How can i store data in a 2d vector?

Question

I have a piece of code where i read a CSV file and prints it contents. Now the issue is that I want to run my code on ESP32 and because of some limitations of micropython I can't upload my file in the spiffs storage. So is there any way I can store the csv file content in the code itself instead of reading it from the outside?

My code:

vector<vector<double> > read_csv(const char *filename)
{
    ifstream read_file(filename);
    vector<vector<double> > csv_data;
    std::string lineStr;
    while (getline(read_file, lineStr))
    {
        stringstream ss(lineStr);
        std::string d;
        vector<double> a_line_data;
        while (getline(ss, d, ','))
        {
            a_line_data.push_back(atof(d.c_str()));
        }
        csv_data.push_back(a_line_data);
    }
  //cout << csv_data << endl;
    return csv_data;
}

This is how i print the contents:

 vector<vector<double> > csv_data = read_csv("A00068.csv");
  // print tests 
  printf("CSV:%d\n", csv_data);
  printf("SIZE:%d\n", csv_data.size());

Your storage seems correct, your printing is definitely not. — Yksisarvinen, Sep 16 '21 at 11:40
you want to hard code the values instead of reading from file? `std::vector> csv_data{ { 0.2,....},{....}, ...};`. — 463035818_is_not_an_ai, Sep 16 '21 at 11:46
@463035818_is_not_a_number There's probably a regex that can do that transformation ;) — Pepijn Kramer, Sep 16 '21 at 12:05
All jokes aside, you're best of just reading the file. Reading looks fine, though I'd use std::stof it can convert std::strings directly. And I'd use range based for loops and cout to output the content of vectors. — Pepijn Kramer, Sep 16 '21 at 12:06
@PKramer probably there is a regex for anything, but this is just too true: https://xkcd.com/1171/ — 463035818_is_not_an_ai, Sep 16 '21 at 12:06

score 1 · Accepted Answer · answered Sep 16 '21 at 12:12

The most obvious possiblities are ....

Hardcode the values directly in your code:

std::vector<std::vector<double>> csv_data{ { 0.2,....},{....}, ...};

Another possiblity is to include your text file as string. For details I refer you to this answer: https://stackoverflow.com/a/25021520/4117728. You basically would add some token in the beginning of the file and at the end, the linked answer suggests this:

R"=====( 0.2, 0.1, ... your numbers
     ... more numbers...
0.42, 3.141)====="

Then include the file like this:

std::string csv_contents =
#include "test.txt"
;

Now you have a string that you need to parse just as you had to parse the file contents before. Hence the only advantage is that now your data can be embedded with the executable instead of being placed in a seperate file. If you worry about cost of doing the parsing then you might consider the alternative mentioned first.

Thanks I stored the values in this way std::vector> csv_data{ { 0.2,....},{....}, ...}; and everything works great. — Vaibhav Vishwakarma, Sep 16 '21 at 18:28

How can i store data in a 2d vector?

1 Answers1