Biblatex - citing from two bibliographies with numeric-comp style (citing order)

Question

This is my first question here. I searched for a very long time for different threads on this topic, but still can't cope with my problem.

I have a document divided into two bibliographies, e.g. books and internet sources. In the text I am quoting using the numeric-comp style. If I try to cite only from one bibliography, everything is fine and it sort the citations in the text correctly in square brackets and good order. However, if I am quoting in one place with using two bibliographies, numeric-comp does not work correctly (it sorts numbers alphabetically, and I want to sort with numbers and compress it to nice view). I have no idea how to do it. I use LuaLaTeX to compile.

Please help and thank you in advance for your interest. Regards John

\documentclass{article}

\usepackage{polski} %słownik łamania wyrazów
\usepackage{polyglossia} %obsługa języków obcych w lualatex i xelatex
\setmainlanguage{polish} %ustawienie języka polskiego w polyglossii

\usepackage{filecontents}
\begin{filecontents}{\literatura.bib}

@article{szymenderski2018simulation,
    title={Simulation of pipeline random response to stray currents effects produced by DC traction system},
    author={Szymenderski, Jan and Machczy{\'n}ski, Wojciech},
    journal={Czasopismo Techniczne},
    %volume={115},
    number={10},
    pages={157--170},
    year={2018},
    publisher={Portal Czasopism Naukowych Ejournals. eu}
    }

@online{random_www,
    title={Random Numbers from Normal Distribution with Specific Mean and Variance},
    url = {https://www.mathworks.com/help/matlab/math/random-numbers-with-specific-mean-and-variance.html},
    urldate = {2019-04-16},
    }

@article{krol2019redukcja,
    title={Redukcja nat{\k{e}}{\.z}enia pola elektrycznego i magnetycznego w otoczeniu napowietrznej linii elektroenergetycznej},
    author={Kr{\'o}l, Krzysztof and Machczy{\'n}ski, Wojciech and Budnik, Krzysztof and Szymenderski, Jan},
    journal={Poznan University of Technology Academic Journals. Electrical Engineering},
    year={2019}
    }

@article{budnik2015voltage,
    title={Voltage induced by currents in power-line sagged conductors in nearby circuits of arbitrary configuration},
    author={Budnik, Krzysztof and Machczy{\'n}ski, Wojciech and Szymenderski, Jan},
    journal={Archives of electrical engineering},
    volume={64},
    number={2},
    year={2015}
    }

\end{filecontents}

\usepackage[style=iso-numeric, citestyle=numeric-comp, sorting=nty, giveninits=true, backend=biber, defernumbers=true]{biblatex}
\addbibresource{\literatura.bib}
\usepackage{csquotes}

\begin{document}

Citing from two bibliographies \cite{krol2019redukcja,random_www,szymenderski2018simulation,budnik2015voltage}

Citing from one bibliography \cite{budnik2015voltage,krol2019redukcja,szymenderski2018simulation}

\printbibheading[title={References}]
\printbibliography[nottype=online, heading=subbibliography, title={Papers}]
\printbibliography[type=online, heading=subbibliography, title={Websites}]

\end{document}

Answer 1

biblatex sorts citations by a global sort ordering. If you have several bibliographies with defernumbers, the global sort ordering may not coincide with the numbering of the references.

In this case it is fairly easy to change the sort order so that it does coincide with the reference numbering, because we only need to make sure that @online entries sort after all other entries. This can be done by adding presort = {zz}, to @online entries via a sourcemap.

\documentclass{article}

\usepackage{polyglossia}
\setmainlanguage{polish}
\usepackage{csquotes}
\usepackage[
  backend=biber, 
  style=iso-numeric,
  citestyle=numeric-comp,
  sorting=nty,
  defernumbers=true,
  giveninits=true,
]{biblatex}

\DeclareSourcemap{
  \maps[datatype=bibtex]{
    \map{
      \pertype{online}
      \step[fieldset=presort, fieldvalue={zz}]
    }
  }
}


\begin{filecontents}[force]{\jobname.bib}
@article{szymenderski2018simulation,
  title   = {Simulation of pipeline random response to stray currents effects produced by DC traction system},
  author  = {Szymenderski, Jan and Machczy{\'n}ski, Wojciech},
  journal = {Czasopismo Techniczne},
  %volume = {115},
  number  = {10},
  pages   = {157--170},
  year    = {2018},
}
@online{random_www,
  title   = {Random Numbers from Normal Distribution with Specific Mean and Variance},
  url     = {https://www.mathworks.com/help/matlab/math/random-numbers-with-specific-mean-and-variance.html},
  urldate = {2019-04-16},
}
@article{krol2019redukcja,
  title   = {Redukcja nat{\k{e}}{\.z}enia pola elektrycznego i magnetycznego
             w otoczeniu napowietrznej linii elektroenergetycznej},
  author  = {Kr{\'o}l, Krzysztof and Machczy{\'n}ski, Wojciech and Budnik, Krzysztof and Szymenderski, Jan},
  journal = {Poznan University of Technology Academic Journals. Electrical Engineering},
  year    = {2019},
}
@article{budnik2015voltage,
  title   = {Voltage induced by currents in power-line sagged conductors
             in nearby circuits of arbitrary configuration},
  author  = {Budnik, Krzysztof and Machczy{\'n}ski, Wojciech and Szymenderski, Jan},
  journal = {Archives of electrical engineering},
  volume  = {64},
  number  = {2},
  year    = {2015},
}
\end{filecontents}
\addbibresource{\jobname.bib}

\begin{document}
Citing from two bibliographies \cite{krol2019redukcja,random_www,szymenderski2018simulation,budnik2015voltage}

Citing from one bibliography \cite{budnik2015voltage,krol2019redukcja,szymenderski2018simulation}

\printbibheading[title={References}]
\printbibliography[nottype=online, heading=subbibliography, title={Papers}]
\printbibliography[type=online, heading=subbibliography, title={Websites}]
\end{document}