Matplotlib plot multiple charts from c++

Question

i use matplotlib from c++ for (debug-)plotting. I want to plot several plots in the same graph. So far i have

template<typename NumericX, typename NumericY>
bool plot(const NumericX const* x, const NumericY const* y, std::size_t size, const std::string& s = "")
{

    PyObject* xlist = PyList_New(size);
    PyObject* ylist = PyList_New(size);
    PyObject* pystring = PyUnicode_FromString(s.c_str());

    for(size_t i = 0; i < size; ++i) {
        PyList_SetItem(xlist, i, PyFloat_FromDouble(x[i]));
        PyList_SetItem(ylist, i, PyFloat_FromDouble(y[i]));
    }

    PyObject* plot_args = PyTuple_New(3);
    PyTuple_SetItem(plot_args, 0, xlist);
    PyTuple_SetItem(plot_args, 1, ylist);
    PyTuple_SetItem(plot_args, 2, pystring);

    PyObject* pymod = PyImport_Import(pyplotname);
    PyObject* s_python_function_plot = PyObject_GetAttrString(pymod, "plot");
    PyObject* res = PyObject_CallObject(s_python_function_plot, plot_args);

    Py_DECREF(xlist);
    Py_DECREF(ylist);
    Py_DECREF(plot_args);
    if(res) Py_DECREF(res);

    return res;
}

but calling

 plot(x_0,_y_0, size_0);
 plot(x_1,_y_1, size_1);
 show(); // just calling matplotlib.show

shows only the first plot. What can i do, to get all the plots?

Gigioz · Accepted Answer · 2020-09-09 13:34:09Z

2

I know it has been a long time since you posted the question and the matplotlib implementation may have improved but still, I have faced your same problem so here is how I coped with it: say your data are (x0,_y_0) and (x_1,_y_1) (let's forget about size_0 and size_1 for the moment). Just call subplot() before any plot():

#include <matplotlibcpp.h>
namespace plt = matplotlibcpp;
plt::subplot(2, 1, 1); // 2 rows, 1 column, first plot
plt::plot(x_0,_y_0);

plt::subplot(2, 1, 2); // 2 rows, 1 column, second plot
plt::plot(x_1,_y_1);
plt::show();

Using just plot() typically displays both traces overlapped in the same graph, like in Python. Hope this can help.

answered Sep 9, 2020 at 13:34

Gigioz

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