# \[AMPL 24523\] 2d variable into c++ matrix
**URL:** https://discuss.ampl.com/t/ampl-24523-2d-variable-into-c-matrix/367
**Category:** Google Group Mirror
**Created:** [February 9, 2023, 4:21pm UTC](https://discuss.ampl.com/t/ampl-24523-2d-variable-into-c-matrix/367 "2023-02-09T16:21:03Z")
**Posts on this page:** 4
**Page:** 1
### Author:  [@Samuele\_Viaro](https://discuss.ampl.com/u/Samuele_Viaro)
#### Post date: [February 9, 2023, 4:21pm UTC](https://discuss.ampl.com/t/ampl-24523-2d-variable-into-c-matrix/367/1 "2023-02-09T16:21:03Z")
Hello,
I have a variable of the form t[j,i]. I would like to save these values into a 2D vector in C++…
I believe I should use the dataframe but I am a bit confuse on how to do it…
Is it possible? Anyone who knows how to do this?
Thank you!
Sam
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### Author:  [@AMPL\_Google\_Group](https://discuss.ampl.com/u/AMPL_Google_Group)
#### Post date: [February 9, 2023, 6:20pm UTC](https://discuss.ampl.com/t/ampl-24523-2d-variable-into-c-matrix/367/2 "2023-02-09T18:20:09Z")
Hi Sam,
You can retrieve the values into a DataFrame with: ampl::DafaFrame df = ampl.getVariable(“t”).getValues();
After that you can use a function such as the following to convert the DataFrame into a vector of vectors.
std::vector\ dataframe\_to\_vector(const ampl::DataFrame &df)
{
std::vector\ data;
int nrows = df.getNumRows();
int ncols = df.getNumCols();
data.reserve(nrows);
for (auto it = df.begin(); it != df.end(); it++)
{
data.push\_back(std::vector(ncols));
for (int i = 0; i \< ncols; i++)
{
data.back()[i] = (\*it)[i].dbl();
}
}
return data;
}
For this type of questions asking on our new forum ([https://discuss.ampl.com/](https://discuss.ampl.com/)) is better since it works a lot better with code.
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### Author:  [@Samuele\_Viaro](https://discuss.ampl.com/u/Samuele_Viaro)
#### Post date: [February 10, 2023, 10:16am UTC](https://discuss.ampl.com/t/ampl-24523-2d-variable-into-c-matrix/367/3 "2023-02-10T10:16:16Z")
Thank you Filipe,
it doesn’t save the values as I expected though…maybe because in my variable t the number of columns depends on the number of rows through the parameter A??
_var t{j in J, i in I: i\<= A[j] } \>= 0;_
do I need to specify the value of A when I save the dataframe??
I apologize if I did not mention this sooner…
Thanks
Sam
---
### Author:  [@AMPL\_Google\_Group](https://discuss.ampl.com/u/AMPL_Google_Group)
#### Post date: [February 13, 2023, 1:06pm UTC](https://discuss.ampl.com/t/ampl-24523-2d-variable-into-c-matrix/367/4 "2023-02-13T13:06:57Z")
Hi Sam,
The DataFrame should have three columns, one of index “i”, one for index “j”, and another for “t[i,j]”. Do you want to load this values into a matrix? You can do that as follows:
for (auto it = df.begin(); it != df.end(); it++)
{
int i = (int) (\*it)[0].dbl();
int j = (int) (\*it)[1].dbl();
double value = (\*it)[2].dbl();
matrix[i][j] = value;
}